Any decent trailer shop that does welding could do the frame work. If the metal is rotted from the inside it will as someone pointed out sound bad if tapped with a metal object. Weld joints not cracked and reasonably solid frame and one can reinforce stress points without any need for expense of a totally new frame.
Checking out the propane
system is routine maintenance so you might find more spider nests, or leaks
on an old one but even new your going to need to check fittings for leaks
with soapy water pretty soon.
On the electric if it ain't broke you can't fix it so this expense is easy to know up front. Plug trailer in and see if stuff works, cheap AC plug tester from big box hardware store and a spare light
bulb or two. Same for the trailer lights
, if they work it only becomes an expense if you want to do the work.
Sand blast the tongue? You can hit that with a small electric sander and wire brush on a drill, then paint
with foam brush or rattle can. Paint
protects metal and metal only needs to be clean enough for the paint
to stick. Decent paint job will look fine on bumper or tongue, it doesn't need to be painted as "fine" as a car or Harley chopper to look good.
Scuffed tire wear or less than approx. 3 inch clearance above wheel to the wheel well are good guideline for "need" an axle
or not. Measure your fist then see how your fist fits above the tire. At this age it should be expected a new axle
will be required but the question is does it need it right away or is it OK for a year or two of use. Axle
done is solid investment that adds value.
Current seller can't say what works and what does not, if you decided to sell it and having used it can say, fridge
all works and axle is only 3 yrs. old it enhances the value, enough to get a good return on the investment somewhat depends on purchase price and market value of one in known good condition. Check out those links from Roy so you know what is a fair offer and how much room you have for adding value from your investments.
Not going to get a "new" 36 year old camper anymore than you are going to get a "new" 1976 Mustang but both can be pretty cool to own.
Question I think you really need to ask is where is your comfort level. Does it all have to be done over to "new" condition for you to feel confident using it, or if it still works are you comfortable with the knowledge something might need repair at some point?
What do you personally have to spend to use and enjoy is the bottom line.