I'd start with the buyers check list in the Resource Document Center here on the site if you haven't already. You're going to get a list of things to check for as long as your arm from all of the helpers here. But, since I'm here first and own a 17' I tell you some of the things I encountered.
You are going to need to roll up your sleeves and crawl under the rig with a flash light
to inspect the frame, plumbing, tanks, and gas lines. Really look at all of the welds on the frame from both sides to see if any are rusted out or cracked. Also look at the two main rails for any breaks, patches or major rust out. I'd recommend a small wire welding brush to clean off the rust and scale so you can inspect them properly. Oh and don't for safety glasses nothing worse that that stuff falling in your face. Check out the axle
for bends, broken leaf springs (if applicable), shackles, etc.. Tanks and plumbing you're looking for cracks, breaks, etc. The collar around the water tank and the gray and black water tanks like to crack and split from age and the plumbing shaking on the road.
Inside look for water stains on the paneling of the floor cabinets and inside the uppers. Also check for heavy rusting on any of the "L" bracket that hold the cabinets to the walls and roof. This will tell you if there is a loose rivet and water leaking in. Fill the fresh water tank with a few gals and pressurize the system. If the pump is flipping on and off, without a faucet open, there's a leak somewhere.
Onto the floor. My Boler
is a 1980 and has a full fiberglass belly with the plywood floor glassed into place on top of the belly pan. Other Bolers have plywood that has been fiberglassed, and there are probably other variations that I am forgetting or not aware of. In my case the plywood is sandwiched between the belly pan and the vinyl flooring making a nice non-breathable situation should water get in under the flooring. You want to check the floor thoroughly for soft spots or spongy places. I had two soft spots that I thought I would be able to do a quick splice and repair but once I started tearing up the vinyl the entire floor was wet through.
Check wiring for shorts or any loose cutoff wires, check lights
etc. on both 12v and 110v. To answer you question about the Ice box, you should still have 110v shore power.
Check in some of the out of the way places for mold and mildew. Also check for rips or tears in the insulation.
I know I've forgotten things that others will expand on. The check list is good, use it. I had all sorts of things that I was going to look at on the 7 hour drive to get mine but when I got there I was so blurry-eyed with excitement I forgot about two thirds of them. Also all of the things I mention are not intended to scare you off your egg but to be aware of what you are getting and possibly negotiating a fair price should something be amiss. As many will vouch, you can pretty much do absolutely anything to these things and it all boils down to your skills, how ambitious you are, time and money. Got a hole in the wrong place? Glass it over and put it in the right place. Got a rotten floor? Tear it out and put in a new one. Holes in the frame? Build a new frame.
OK. I'll stop. Good luck. I hope it is exactly what you are looking for. They are great fun to play with.