Is it plugged into electric when it's setting? If not, you may need to use your battery disconnects so they don't have any parasitic load draining them.. Also you probably didn't let it run long enough before when you started it.. It should be taken out on the road and run for at lease 20 mile before shutting it down.. That way all systems get to come up to working temps..
If you're going to let it set that long I would get electric to it to keep the house batteries charged.. You will also need something like the "Trickle-Start" to keep the chassis batteries up, because they won't be charged by the inverter, unless it is set-up from the factory to do so.. Mike Mathews..