Welcome to the forum, Dustyglass.
Water, water, water ...that's what I tell others to look for when in the buying process of an older motorhome.
1. Check for water leaks and check for mold. Inspect everywhere you can for evidence of water and/or mold ...the entire ceiling, walls, inside cabinets and closets (use a flashlight). Seeing any evidence of water or mold can lead to major hidden problems so be aware and curious about any of theses signs.
2. Same with floors. Check all floors for evidence of rot. Jump up and down in places that are suspect like the bathroom area. Also check the walls to make sure they don't have any give when pushing on them. Check around the windows and especially the windshield for evidence of leaks.
3. Get up on the roof and inspect the caulking to make sure everything is sealed. A well-maintained roof is a good sign that the prior owner has taken precautions not to allow any water to get inside. While you're up on the roof, make sure it feels stable. Again, soft spots or feeling a lot of give might indicate rot, water damage, etc.
If you can get chassis maintenance records, that will be a very good sign that shows that the prior owner took some pride in the care of mechanical items ...engine, transmission, brakes, suspension, etc.
Check tires ...their age and condition.
So even if the motorhome you're purchasing is over 20 years old, it can still give many more years of service if it was well maintained over those years. If not, as you can imagine, you will have problems with it sooner or later.
Here is an article that gives the same advice on water but also a few other things to check as it's written keeping in mind a motorhome in that 20-year old range too:
Buying An Older Used Motorhome: How To Inspect It Before Purchase (A Checklist)
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