Has vehicle conversion been re-classified as an RV?
If not, I doubt Good Sam Club will cover it either. What your going though isn't uncommon on truck conversions. It the vehicle is not titled as an RV, you'll need to contact your DMV to get it so. They should have a list of things you'll need to have in place to make it happen. Once it's titled as an RV, you shouldn't have any problems.
It doesn't matter what the vehicle title says it is, its the VIN number that insurance companies use to determine what their having to insure. Once the conversion is complete and certified as an RV, a new VIN will be assigned to the truck defining it as such.
Double check with the insurance company to make sure the VIN number their working with is correct. An single incorrect number or letter can really cause problems in determining what the GVWR is.