I'd bet if your silnylon sewing skills were up to it that would be a great way to try it out.

Not sure I'd put fleece underneath, just more crap to dry out. I'm thinking I do like I do with my socks, which is to put them over my polypro liners only (to keep from having foot problems,) and then put all the insulation outside, so me, if I were to do it (and I haven't) I'd put them over a comfortable poly base layer, and then everything overtop. When I get into camp, strip, and change our the base layer. Then you only have a poly base layer to switch out when sweaty, and that's almost always easy to dry out, or if you have to put it on moist to go the next day isn't so bad - particularly if you're in "wet suit mode" all day
anyway.

Just judging on how I do with silnylon VBL socks in boots anyway.. Geez you've almost
got me tempted to try it this winter, but I've always avoided it thanks to some horrid nights in a vbl bag liner (I'm a clausterphobic sleeper and a sweater..)