You start by knowing the fully loaded curb weight of your minivan. That's loaded, full fuel tank, full of passengers that would normally be traveling with the towed trailer. It'll cost you $5-$6 to run it across a scale.
Then you need to know your GCVW (gross combined vehicle weight) in your owners handbook or in your door jamb. You subtract the curb weight of your van from the GCVW and that tells you how much weight you have left to tow.
That tow weight would include the weight of the trailer, the weight of the hitch and all the items in the trailer.
My guess is it's going to be a very small trailer. You want to try to stay away from trailers with those little tiny donut tires/wheels. You want something with at least a 13" tire/wheel and preferrably 14". The smaller the tire/wheel, the faster it turns, the hotter the bearings get. Also, the larger tires/wheels are easier to located if you had an emergency on the road.
Home Depot, Lowes, etc. has small utility trailers that are pretty light weight. Be sure you get the ratchet type tie down straps (much easier to use and release) and I prefer to go oversize on them (larger straps than I think I'll need). I wouldn't want a load to come undone on me and end up having those behind me crash because of it.
You may want to get a large, heavy duty tarp with the tie down bungee cords for it, to cover your load. That way, if you get caught in bad weather at least it's somewhat protected and from UV in the direct sun.
Hope this helps you make a better educated decision.
