It's a trade off. 6AWG wire will be around $1.30/ft and you have to run 2 wires and you need to fuse it. It's basically a question of what way is cheaper given what is already installed on the boat. If the boat already has ACR's I would likely run DC. Since he already has a 3 bank charger, if he doesn't have ACRs, the inverter way is probably best.
My parents used to do something like this when they towed their boat back from Canada to California with their Norcold full of fish.
If we are talking anything less than 10 hours of driving or nothing is on in the boat like a fridge, it's not worth doing anything.