The checklist is great, but it assumes you're already a trailer expert and just need a list to remind you what to look at. I don't think it's much help for a beginner.
The easy answer is: it's complicated.
You'll find out really quickly that so many things can go wrong with a used purchase, especially one this old, that it threatens to rob all the fun from the idea of buying and owning a camper.
But a lot of us have been there, done that, spent tons of money and time fixing issues we never even knew to look for.
Things that, if the current owner hasn't recently replaced will quite possibly need replacing:
Things that will likely need servicing, if not replacing:
(bearings and suspension)
Brake lights/turn signals
Anything else? Those, I think, are the basics. There are all sorts of other things, depending on whether this camper has them or not including a fridge
, heater, water pump.
Campers are a lot of work even when they're in great condition. Just the way they are. But you can reduce the amount of work if you don't need most of the amenities of a trailer.
Most people here are older and have some amount of disposable income or repair skills, and they aren't interested in "chancing" anything. So if the frame is weak, it's getting replaced or repaired. If there's a small spot of rotted floor, they're replacing the entire floor. Any little crack in the fiberglass or not-completely-straight door and there's a month long project of tearing out the interior and fixing fiberglass, fabricating frames and all sorts of clamps and tools out, etc.
But there are also a lot of people out there just making due with the condition their trailer is in, so long as it's more or less safe to pull down the road.
If you need a nice bed and place to hang out, but don't need a stove plumbed in to the camper, or heat, or a water system, and are ok with portable LED lights
...all you need is a more or less water tight shell, a solid frame and good tires
and wheel bearings.
So...do you, or do you know someone who has an eye for those things? To go look at a trailer with no experience of what you're looking for is taking a big chance.
All that said, it's a great idea. When you do find a good trailer and go through whatever trials it takes (if any) to get it road worthy, you're going to have a great time on that trip.
Be sure to keep an eye on this site