Welcome to the forums. We've worked on only '60's models, but we know many folks with '70's trailers and they love them. I think the Tradewind is a nice size, small enough to get around on some of your roads, beyond the M-1. We have the model smaller and the one larger. I'm sure you'll get a number of recommendations from others, but, if it were me, you might want to:
Take a good look at the frame anywhere it is exposed. Your looking for significant corrosion or wastage. Surface rust is not a major concern.
Look at the axles, if possible, jack up one or each side and see if the axle has travel (movement) downward of a couple of inches. If it doesn't move, you'll be replacing axles.
Check the floor for soft spots, especially near the door, front corners and in the rear near the bath. Soft floors mean leakage has been occurring and rotting the floor. Replacing some sections is not unheard of, but if it is extensive, that could dictate a full shell off project. It can also suggest possible frame damage.
Ask to run all appliances. If there are any excuses not to, consider every appliance you can't verify to need replaced and consider that in your offer.
Look over the exterior, minor dents and scratches are normal. Major dents, especially at a riveted seam are more of a concern. Windows should be intact with glass and operate.
Check the wheels and tires and ask about maintenance. When were the brakes changed? When were the bearings repacked? When was it last used? Check the running lights and brakes.
I also think there is a thread here on the forums somewhere on what to look for when purchasing.
Roy and Marie