Originally Posted by
UnCruel
.... The way the tent bag is made, it is the poles, rather than the tent fabric, that are exposed to potential damage, and they are likely to tolerate more abuse, but I don't want my nice things destroyed in any case.
The poles may make the bag a bit stiffer, less likely to sag, but if the poles in the bag are a problem you might be able to strap the poles to the bike top tube instead if you have some velcro straps.
A piece of cardboard from a cardboard box can make the bag stiffer if you need the extra stiffness on the bottom. The Carradice bag I showed behind my saddle, I put some coroplast (essentially a plastic form of cardboard) in the bottom of that bag to make it less likely to sag.
With this sort of project, you need to be creative and anticipate problems before they happen.