Heres the idea. An A-frame tarp (tube tent without the floor) with a back panel. make it a bit longer for better protection. make it out of a painters tarp and duct tape(sticks surprisingly well!). This is to be used over an air mattress sized 74" x 39" x 8.5" with no side room and some front porch.
Questions for the wise:
1. the mattress will be pretty much up against the rear panel. make the panel wide enough that it can be pitched against the ground here, or integrate the mattress and tape 'em together?
also, height of this? keeping in mind the 8.5" taken up by the mattress.
2. the rear trekking pole, inside or outside?
3. length. in good weather, it will be pitched with a trekking pole at the edge of the tarp on the front end, and the corners can staked directly or tied off at a lower angle. In bad weather, the idea is that the pole can be moved back along the ridge-line so that the edge(where it was) can be staked down. I'll make two tie-outs the same distance back on the edges as well. With a shortened pole, and a long enough tarp, this could go straight to the ground. and a full wall could be made, sound like a good idea? This would we tricky to enter/exit, and would make good hieght at the other end more important.
4. considering the fragile materials, is it worth making a ridge-line? if it had two loops in it and was sandwiched into the duct tape with the plastic sheet it would be simple and the trekking poles could attach there. if the storm pitching was used the front pole could be flipped so the blunt handle end was on the tarp, and the look could be staked down.

also, a guyline idea! Not for this shelter, but I thought of an interesting way to tension guylines from inside the tarp/whatever. It needs grommets.
step 1. tie one end of line to stake.
step 2. thread free end through grommet and then through a cordlock on the inside of the tarp.
step 3. don't get wet tightening your guylines when your sil shelter sags during that rainstorm.

I've got a lot of things on my list, but I have time tomorrow so I might try making one, or in a few months we'll see how it works.

Are you talking about the canvas or plastic tarp?

Canvas tarp. Way too heavy. Absorbs moisture. Not waterproof.

Plastic sheet. Very fragile.

I would look to other materials, personally.

Now, I think I understand your guy line idea. Implemented correctly, I think it could work nicely.

8.5" taken up by a mattress?

--B.G.--

the plastic sheets. Yes, they are more fragile than most fabric used for tents, but if you get one of the thicker ones(maybe 2.5 or 3 mm?) and reinforce it properly with duct tape it hold up quite well. Its also totally waterproof. I'm not too worried about condensation, its just going to be for one nighters, and if it looks like it will be really wet I probably just won't go.

Yes, the mattress is big, I wish it wasn't so tall. I'm going to have it at school anyway, so I'd rather not have to bring a pad in addition to that, and its super comfy and fits two if you need to.

edit: also, what about making a catenary ridgeline?

Edited by wjsawyer on 09/02/2010 05:22:00 MDT.

doesn't make sense with this material. Won't last you more than a few nights out anyhow. Why spend the time on it?

If your mattress is touching the sides of your tarp, it will get wet. Just something to keep in mind.

The catenary ridge line will do you no good in this application. You will not be able to pull the 2.5 or 3 mil plastic taut enough to take advantage. If you are looking for super cheap, look into scrap Tyvek from a construction site. Ask before taking, but usually you can find some. However, Tyvek is not waterproof. It is just resistant. You could always bond the super thin painter's tarp to the underside of the Tyvek. =) It would not hold up for long, but would be able to be pitched tighter and would still be ::ahem:: relatively light.

Rigged? Maybe. Durable? Meh. Cheap? Definitely. Light? Light-ish.

Seems like a lot of trouble either way, but if funds are the main driving force, DON'T let that keep you from the great outdoors. HYOH!

I think 2.5-3 mil stuff is more durable than most of the other posters in this thread. I use the 0.7 mil stuff as a ground sheet and I get a decent number of nights out of that. I think you could get a season out of the 3mm stuff if you were careful.

For the ridgeline, I would grommets. Perhaps use several grommets to spread out the force. Maybe 2-4 grommets on each end. Then I would do a grommet at each corner and 1-3 along each edge to hold it down. Maybe use a bit of bungie cordage/shock cord to buffer out any spikes in strain caused by high winds or tripping over the lines. You could attach a foot of bungie cordage and then attach regular cordage to that and use tensioners on that cordage.

> The catenary ridge line will do you no good in this application. You will not be able to pull the 2.5 or 3 mil plastic taut enough to take advantage.

If you reinforced the ridgeline with 3M's 2120 transparent duct tape (see my thread on a MYOG LDPE tarp), that shouldn't be an issue. I don't think the effort is worth it on such a "temp" shelter though.

Thanks for all the responses.
Michael, How would you go about taping the curve? I'm assuming the 3M tape that you mention is about 2" wide and would wrinkle or make the plastic wrinkle on the curve.

Del, You are complicating a simple thing. Although tyvek is free compared to a $5 tarp… What ifyou use a DWR spray on the tyvek too? or try to give it a thin coat of silicone?

Dan, Finally some agreement on the durability! just keep sharp things away!
Can you go into more detail on your grommet method for the ridgeline? do you mean put a few on the end for the tie-out, or attach two sheets using grommets instead of tape or something else?

I got a 9' by 12' 3 mil sheet and most of a roll of duct tape and got to work today. For I made two side panels, 9' long, 5' at one end and 5'6" on the other. This makes it wide enough to keep off the mattress. I joined the two with a sandwich of duct tape, and I added a thin cord into it. This way when Its pitched this 'ridgeline' takes most of the tension. I did two grommet corners with lots of duct tape reinforcement and those came out very well. I ran out of tape and time before I could finish the back panel, but its coming together well, I'll try to get some pics up. In low light it almost looks like cuben!

Regarding the grommets, instead of putting one grommet in the plastic and tying your guyline to that you could put multiple grommets in the plastic so that it's not pulling so hard on one spot. You could put two grommets in the plastic about an inch or two apart and then use a short string to connect things. Then you could tie your guyline on a sliding knot to that string, so that it naturally evens out the strain between the two guylines. Taking it a step further, you could do 3 or 4 grommets with a similar system to even out the strain. 3 might be a good number because you could have one right at the true ridge so you get a fully taut ridgeline. Does that make sense? I haven't tried this...I'm just speculating on ways to disperse the force. Larger grommets would also be less prone to tearing out that smaller ones.

Dan, your suggestions are good, but theoretical. By the time the original poster gets all of this plastic and tape and grommets and guylines and everything, it is going to weigh a ton.

In the lightweight category, I just can't see it.

I saw a simple plastic sheet deployed this way one time. The user simply tied one cord between two trees, and the plastic sheet went over it. Rocks held down the corners in an A-frame configuration. Period.

--B.G.--

3-4 medium sized (ie. 5/16") grommets per side on the ridgeline plus one at each corner plus 2 more along the two sides (14-16 grommets) would weigh 0.78oz if you used metal ones and likely less with plastic. That's nothing compared to the weight of this 9' x 10' 3 mil sheet of plastic.

If that's too heavy, do 2 at each of the ridgeline, 1 at each corner and 1 more along the two sides for a total of 10 grommets or ~0.5oz. This is probably a nice simple yet reasonably strong way to go in theory.

Edited by dandydan on 09/03/2010 02:10:23 MDT.

Will,
Yes the tape is 1.88" but it is pretty flexible just like most duct tapes so on such a slight curve I don't think you'd have much problem with wrinkles. Again though, it sounds like this is pretty much just an occasional overnight shelter you'll be using while in college and likely replacing each season so worrying about a cat cut doesn't make sense (to me).

As for grommets, I'd recommend you use tape for tieouts also. You can see the LDPE tarp thread I already mentioned or this thread where I got the idea from on how to accomplish those effectively.

> Dan, your suggestions are good, but theoretical. By the time the original poster gets all of this plastic and tape and grommets and guylines and everything, it is going to weigh a ton.

That was my first thought about such a tarp... but then the OP is also considering carrying a 79"x39"x8.5" airbed. So I guess weight and bulk don't seem to be too high on the list of priorities...