I have been using a tarp for several years, but, bugs at night have always been a headache. Especially on warmer summer nights, mosquitoes near wet areas can travel a ways to find you...sometimes as much as a quarter mile.
I have developed a layered defense against most bugs, averaging only one bite per 48 hour period, on average, even in black fly season. Usually while paddling, and during the day when they are most active. Deer flies are often nearly indefensible, but not out when there is no sun or very inactive.
1) Tarp - While primarily to protect me against rain/cold, it works fairly well as a barrier to bugs. However, they have a way of slipping under the edges and in any doorways you have setup.
2) Permethrin - This will stop most bugs, but is especially helpfull on clothing. While not really a repellant, bugs avoid it, anyway. I believe that instinct tells them it will kill them. Read warnings and decide for yourself.
3) DEET - On exposed skin, I use a drop or two and spread it around real good. Not Recommended, since it IS a carcinogen, but for many, a few times per year probably won't give you cancer. Read warnings and decide for yourself.
4) Clothing - long johns or the like will deter most biting bugs. Mosquitoes can bite through this layer if you give them a little time. I do not soak bottoms, socks or underwear in permethrin.
5) Sleeping Bag - Generally, a light sleeping bag is bug proof.
6) A small piece of mesh over my head in warm weather. This deters biting insects, but mosquitoes can bite through a lot of fabrics. Again, treated with permethrin, it does a good job, even if it is just getting even...bloody things. A small tent like structure can be tied up to a loop in the tarp with a pebble.
7) For very warm months, I bring a full mesh tent. This is a compromise between weight and utility. If I know I will be headed into wetter areas and nights will be warm, I bring it. This will also deter larger critters: spiders, scorpions, snakes, 'coons, etc. This is in place of the mesh piece over my head, which I often roll out of.
Durring the day, my long sleeved base layer top and hiking pants (both treated with permethrin) usually does the job well enough to avoid most bites. My hands often get washed clean, paddling. DEET needs to be reapplied fairly often (2-3 times per day)on canoe trips. My hat gets treated with permethrin, also. Then the brim gets a heavy coating of DEET. At night, the hat holds my pocket gear (knife, ID, glasses, etc) and placed near my head.
What do you use?