If you mean you have the key in the "accessories only" position, so the radio and windows will work, but not the engine or glowplugs, then there shouldn't be much electrical drain if you turn off the sterio and HVAC fan and any other items that have an on/of switch, such as heated seats, DVD player and navigation system.
10 years ago, the Owner's Guide for my '99 said all I had to do was put the tranny and manual transfer case shifter in the neutral position to tow my pickup behind a motorhome. So that should still work. What does the '08 Owner's Guide say?
The electrical connection between motorhome and toad runs lights and turn signals on the toad, but it could also contain a 12-volt hot wire. When towing an RV trailer, the 6-wire or 7-wire trailer connector includes a hot wire that is used as the battery charger/maintainer, so I would think you could hook it up to have the motorhome altenator also charge the batteries in the toad. If I had that much money tied up in a motorhome and toad, I think I'd probably figure out a way to do that.
