My '99 is the same way. Consequently, I will be installing a battery parallel switch so the engine can be started from the fully charged 8D house batteries if necessary.
In order to keep the wiring simple, the 'hot' lead of the house battery will go to one side of the relay and the other side will go to the 'hot' lead of the chassis battery. Actuation of the solenoid will be by running a 'hot' lead from the house battery to 1 terminal and a momentarily switched ground to the other. That way I only have to run 1 wire. A 200 Amp relay can be bought for $42.00, which should be plenty for starting an easily started engine, which, fortunately, mine is. BTW, the relay is what Fleetwood and Winnebago use for their "Emergency" start purpose.
I'll also be doing a few other things to make the beast more 'Driver-friendly'.
1. A DPST switch to energize the Cruise or Pac-Brake. That way they can't both be powered at the same time (Cruise on = Pac-brake off/Pac-brake on = Cruise off).
2. Rocker switch for the heated mirrors (rather than that stupid little toggle switch).
3. Red blinking LED to indicate mirror heat is on and to remind me to turn it off.
4. Green LED to indicate "Economy" mode is active (I can't see the LED on the pad while I'm driving).
5. Yellow LED to indicate Pac-brake is active.
I guess I've been around big boats too long and like to 'Tinker'.
Bob (Squidly Down Under) & Peg - 2013 Ford Focus pushing a 2011 Phoenix Cruiser 2552S
"In God we trust" to preserve our country and bring our Troops safely home.
Carry on, regardless..................