Good luck checking out your new Burro
. I bought a 1983 Burro
about 3 months ago and I've been fixing it up. I love it.
From my limited experience the floor can be rotted out anywhere, but the most likely area will likely be inside the wheel wells (check plywood behind and along the tires), and in my case by the front door. If worse comes to worse you can replace the wood floor -- I just replaced some of the plywood near the door in mine since the rest was OK. The 1983 windows
aren't the best but with a little butly tape you can take them out and reseal them pretty easily.
The frame will be rusted to some degree but check to be sure all the welds are solid (not cracked). The torsion axle
(suspension system) may need replacements (check if the trailer is sagging) - mine was OK even though it was 1983. If you have to replace the axle
it'll cost about $500.
If the light
and electric components don't work they are easily fixable. I rewired everything, put in LED lights
(outside and inside), a new 12V converter and solar
Mine looked like hell when I bought it but after a little work it looks great. So look past ugly features (e.g. cabinets, ceiling cover, floor covering, cushions) because those are all easily fixable.
Best of luck.