any sort of water leak is bad . Look in closets and dark corners. Check roof for deteriorated caulking, tears in the roof etc. Realize that no matter how much tread on the tires if the tires are more than 5-6 years old they need replacing, Sitting is the worst thing for tires.
Does the unit look beat if so pass. Ask for maintenance records. If the guy has them it is usually a good sign.If fiberglass exterior look for bubbling of the fiberglass which appears as waves. This is an indication of a leak and the layers of siding separating
What do you plan to pull the trailer with?
Is it within your cargo capacity as well as your towing capacity. Those are 2 separate numbers and both are important. The cargo capacity is on a sticker somewhere in the vehicle. That is the total that your vehicle can safely handle and includes anything you put in or on the tow vehicle. You, your companion, the dog, Suitcases etc. Now find the gross weight of the trailer not net weight but gross weight and figure 12-15% of the trailer weight will be placed on the tow vehicle. Example a 10,000 LB gross weight trailer puts between 1200 to 1500 pounds on the tow vehicle lessening your cargo capacity by that amount
The problem is the "qualified inspector" does not guaranty the quality his work so if he misses something you are out. There was a long thread recently by a guy who paid to have his new purchase inspected and the inspector missed many obvious flaws.
Better a mobile repair guy who you pay a couple of hours labor to.
In fact one of the inspection services will not even get on your roof to inspect it.
The NVRIA National Recreational Vehicle Inspectors Association states
The National Recreational Vehicle Inspectors Association, Inc. does not make any representation or warranty as to the quality of RV Inspections done by its RV inspector members.