The reason I was thinking about using extra cables for TC is not charging, as we usually drive long enough to charge camper battery via bumper plug, but using truck batteries for rare occasions.
It happen to us couple "winters" ago in California, where 60F night called for furnace use. Single battery went low at 4 AM and even new truck has remote start, the option is not activating trailer relay, so I had to go to truck and insert the key.
Now would I have easy way to run a wire to truck 2 batteries (I think even 8 ga would be overkill for the purpose) - I would be comfy without the hassle of carrying 2nd camper battery for once in 3 years use.
Obviously running camper with truck batteries brings worry about starting power, but that is where 20 lb generator comes very handy, not to mention that the cell phone power pack can give 50 amp boost.
