newer astros have 6 lug somewhere around mid 2000's they switched I think. what dealer has that camper at it? Wouldn't mind seeing pictures of it!
Wouldn't it be easier to get a low mileage heavy duty frame (like from a M1008 CUCV) and mount the van body etc on it?
I had an 86 Chevy converted by Pathfinder, which was pretty well done.
Their are places that could help you convert yours but you are better off buying one already done.
Sometimes I wish I still had mine.
This is an interesting site for looking at 4wd vans for sale.
http://www.thundersgarage.com/4x4vans4sale.html
The 4x4 van gallery is pretty good.
http://www.thundersgarage.com/4x4vansg1.html