I would say to protect the frame, all you need to do it make sure it is painted good. Maybe paint it every year to make sure. As for electrical connections make sure the insulation of the wires is/are in good shape. Also, where there is a connection, try some heat shrinking material to protect the connection - sometimes electricial tape will loosen and come off.
And maybe just get the under coating done?? Or do it yourself. There are various companies with products for under coating.
As for rust that has already started, the best way to removed it is to sand it off, or to cut out the bad spot (obvisouly don't do this to the frame). Also, products like POR-15 can be used to paint over rust and it suppose to stop it from spreading.
Remember, always use a rust inhibiting paint, because it will keep rust back better then regular paint.
You might also must to look into under coating that you can by in a spray bomb or rattle can. I've used products like that before, and on target areas it works well. Just shoot the stuff on. It is a tar substance that explands when it is applied. Like I said it is good for spot applications.
But to be sure, I'd say you should get the whole under carriage undercoated. I've seen what can happen to vehicles here (we use salt up here) and even newer vehicles have rust problems underneath already - I'd expect the same thing would happen to an RV.
- Jeff L.