Like randy noted...look for leaks.
Lots of rust on the frig cooling unit, no ammonia smell.
Check the roof and roof seam and caulking.
Check the date code on the tires...no more than 5 years old.
Then you need to check the GVWR on the trailer and make sure your loaded Yukon is rated to tow the weight and can handle the hitch weight.
Read this site for info on weights and ratings.
Once you pass the weight test (do not believe the RV sales person) you will need a good weight distributing hitch with sway control and a brake controller. I like the Reese Dual Cam Straitline and the MaxBrake controller.
Ken