A few things I came up with:
- Extra fuel - I have carried extra fuel but honestly have found that stopping when you are around half, or higher if this is the last stop for a while you do not need a lot of extra fuel. I have a policy that I fill up when it is convenient or close to stopping for the night and I have yet to get low.
- Batteries - carrying too many batteries is a waste of weight and space. Get a couple good solar panels, a direct line from the alternator or even a small generator for those really big draw times. Heavy battery packs cost in lower MPG and less weight available. If you are also having a TT then you have two roofs to use to gather solar and unless you are a real power user you will be topped up in no time.
I understand you idea and have thought of it myself One thing to think about is you do not necessarily need two fridges, bathrooms, showers, etc, etc. You could shed some weight by not doubling up on everything. Load the TCer with what you need for a day or two and unload when you come back.