Hi Matt,
The intial purchase, and installation of a NG kit is NOT cheap. It may be cheaper to convert to Megasquirt EFI, and you'll get better mileage. I have a dual fuel NG/gasoline kit on my 81 Dodge van. It has turned out to be very economical, and reliable to run. My van has a single carb, with the NG mixer on top. Your VW van is probably dual carbs. So, you will need two mixers, or have to convert to a single carb.
The tanks for NG are large. You have to find a place to mount them. I'm sure you will not want them inside your camper, taking up valuable space. Is there room to mount them on the bottom of the vehicle?
My van is for sale, cheap! If you need NG parts, it would be cheaper to buy the van, and take the parts you need, then to buy a new NG kit. Also, it would best to have someone with NG vehicle experience do the hook up, as lots of specialized tools, and knowledge are required. I think the Yellow Pages has a listing for Natural Gas Conversions, maybe wise to phone around and get some info.
Check out Landi-Renzo website
HERE for info about NG kits / parts. These guys are the main manufacturers of NG kits.