My wife and I started off with an older trailer. It was a fixer-upper.
The projects never ended. Weekends were spent working on the trailer. Once we got it all done, it still leaked. It was also drafty inside. The first time we took our little one camping, we decided to buy a newer trailer that was project free. Went from a 1979 crapcan to a 2007 Jayco 20BH. We've never regretted our current purchase.
The one good thing to come out of the old trailer? I knew what problems to look for. I knew the signs (stains, things covered up, etc.) to look for and avoid. I also learned how cheaply trailers are made. And I hate staples!
My in-laws have a 1970 trailer. It is a continual project. Originally, the trailer just dumped its grey water on the ground - it never had a holding tank for grey. My father-in-law ended up plumbing it into the black tank to stay legal.
As someone who has 'been-there-done-that', walk away. Its hard to resist the price "Its only $x!". But add up the countless weekends, all the trips to the hardware store, and that $x turns into $x*3 pretty fast. And it still won't be that great.