I forgot to update this thread. I did in fact run this wire. I ended up using a maxi fuse (50 amp) because the breakers were expensive and the fuses that are feeding my stereo in my trucks have been there for a decade or more and are still going strong. If I blow the maxi fuse somehow, it's easy to get a replacement as well.
I went with 8 AWG wire. Any bigger than that and the price went up pretty fast and the 8 can handle enough to do the job.
I soldered on all of the lugs and the splice, although I agree that the solder point between the 8 AWG and 10 AWG at the camper connector was a pain. fortunately I have a pretty good butane torch and was able to get it hot enough.
I used a golf cart continuous duty solenoid. It looks a lot like a ford solenoid although it has a separate ground terminal rather than grounding through the mounts.
I believe the wire I used to trigger the solenoid to close is the cigarette lighter circuit that comes on with the key.
Between that and fixing my small solar panel I look forward to NOT! dead batteries when I arrive at my next destination to camp.
