Dan, I tried that, but the drysack I got, the Granite Gear cuben fiber Uberlight large size, is 18L, 6 x 8.75 x 22.5".
When filled, this produces a solid cylinder, too long to fit sideways. I can just stuff it tighter and it could fit, but that doesn't solve the issue of trying to protect the bear can. That method actually causes the bear can to really push out at the front, leaving the pack vulnerable with the first rock it is leaned against.
So, I do plan to lay it sideways, if needed, it just needs to have enough material to allow for the whole thing to really flatten out.
I had planned to wrap the can with my ProLite Plus, and that worked great. But I just got the Neoair, so that method won't work.
Angelo, while MLD does state that custom sizing is not available, I'll get with the others to see if they might do it, good idea.