Once you identify the chassis used under the coach you usually can readily determine the GCWR and GVWR, which govern the max towing capacity. The only other variable is the receiver hitch itself and that is usually labeled and/r stamped with a rating or hitch class, e.g. Class IV.
Generally speaking, older gas coaches will have a 3000-4000 lb max towing capacity and diesels will be 4000-10,000 lbs, depending on the chassis used. Even new gas coaches usually have a 4000 lb hitch and tow rating. Your minivan is probably around 3600-4100 lbs unless you have one of the earliest model Dodge/Plymouths which I believe were somewhat lighter. Jeep CJ's are light enough to tow with most anything, but Cherokees, Grand Cherokees, Wagoneers, etc. will all probably exceed a gas coach's towing capacity.