Congratulations on getting your expando to open up! I've always been curious about these kinds of bodies. I've had a couple of shop vans, and in both cases the windows weren't in great shape because the wooden portions dried up, shrunk, and pulled away from the metal frames, so that the windows were falling apart and didn't seal well. I always suspected that an expansible van body wouldn't keep out the rain too well after 25+ years of use and abuse, so I'm interested in hearing how well yours seals up, and whether it'll take a bunch of work to renovate it.
For some reason, I have some inexplicable interest in things like expansible vans, commo shelters, and so forth. A friend of mine has one of the parts storage semi-trailers that doesn't expand like yours, but the sides fold open to provide more work area. It looks really cool. There's also one of the M944A1 SEORTM "batwing" trucks coming up at GL soon. It's tempting me, but it looks like the machine tools have been stripped out, so hopefully I'll be able to resist the urge to bid on it!