What does your owner's manual say about the GCWR of your Chevy van?
You need to know equipment, because towing capacities might depend on which engine, which rear axle ratio, and factory towing packages. Working with 2015 model year ratings, Express 2500/3500 towing capacity could be as high as 10,000 pounds (e.g. empty HD cargo van with 6.0 V8), and something over 7000 for the smaller V8. But the weight of the conversion, and the stuff you are carrying, might cut into that as much as 3000 pounds.
You can tow anything up to that weight, though anything over 1500 pounds should probably have its own braking while being towed. You can tow flat, you can tow on a dolly, you can tow on a trailer. What you can tow flat depends on what you are willing to do to prepare it for towing. What you can tow on a dolly depends on it being dolly towable (a lot of AWD and RWD vehicles are not). What you can to on a trailer will depend on how much rear axle capacity you have left to handle tongue weight, a Roadtrek 210 might already be pretty well loaded on the rear.
If you have the 6.0 V8 you can probably flat tow anything you see other motorhomes flat towing.
Tom Test
Itasca Spirit 29B