I would caution totally disconnecting the truck start battery. There are many things running associated with the truck electronics and when you disconnect the battery all of those will reset to some state. Then when you re-connect the battery the truck computers are suppose to learn all over again and in my case that did not happen for the truck engine idle. My truck engine would die every time I would stop at a stop sign etc... The new trucks have no manual way it appears to raise the engine idle. On mine it is all done with electronics. I ended up having to go to Ford to have their diagnostic machine reset my truck computers which was a $90 charge. I certainly will not disconnect my truck start battery again for any long length of time...
In your case I would investigate what is being disconnected with the RV SYSTEM and make sure all of that is disconnected when the disconnect is activated... Unlike deep cycle batteries all it takes is ONE truck start battery total discharge and you may have to replace the battery. That has been my case at any rate.
Roy and Carolyn
I claim Horse Creek Country in Southern Ill - Momabear is from North Texas
We live in King George VA
RETIRED DOD DOAF DON CONTRACTOR Electronics Tech 42YRS
"We're burning daylight" - John Wayne
2008 STARCRAFT 14RT OFF-ROAD POPUP with PD9260C and three 85AH 12VDC batteries
2010 F150 FX4 5.4 GAS with 3.73 gears - Super Cab - Towing Package - 2KW Honda EU2000i Gen
K9PHT (since 1957) 146.52Mhz
"We always have a PLAN B"