I agree with the driveway campout. It's a good way to try out appliances, etc. and make sure everything works to suit your needs.
I would also take it in to a trusted mechanic to get checked out (cab & chassis) - don't forget to have them check the fuel lines (they will deteriorate with age also).
If you're not a handy type person, now is a good time to find a good RV repair shop - have them check the propane lines, stove, heater and fridge for propane leaks. They should be able to help you out with how to operate they systems and answer questions you may have.