I would personally try to avoid bolting anything to the van exterior skin. But that's just me.
Theres a category of external bags that can be adapted to hang off nearly anything. The most notable might be the "Trasharoo" product. You'll want to make sure it has good UV resistance or its likely to deteriorate in a year or two. The Trasharoo is focused on holding trash. But there are other versions that have more pockets and divided storage compartments. Good ones can get pretty expensive for what they are.
If you bolted something like a molle panel to the rear door, you could attach almost anything, soft or hard.