Another point of view:
The front wall of my box catches the most wind and therefore is the coldest and noisiest. So here is how I treated it:
1) one layer of carpet padding
2) one layer of quilt batting
3) matching fabric and upholstery tacks from hobby lobby
It goes up (and down) real easy, so changing out fabric with the fickle times of fashion is not a problem. The padding gives a nice look (personal preference), as well as insulation. From an acoustic standpoint, the carpet padding absorbs structural noises, and the batting will help by lowering the overall volume inside. I used upholstery fabric (I think its type of linen), so the batting would work properly. Vinyl will act more like a sound barrier that blocks outside sounds. I used vinyl over the accordion gasket between the cab and the living space because I needed the extra sound barrier.
sidenote: I took geofkaye's advice when buying gear for my conversion, and I purchased most everything direct from the manufacturers. Saved thousands!
Doc Weaver '98 Freightliner FL60 pseudo toy hauler