Options, lots of options!
If you want to totally shut down power draining from the coach batteries, the easy one seems to be removing the one long ground cable from the negative post in your picture. We can't see which of the three black cables goes direct to the ground bus, so some looking for which of the three will be needed?
the negative cable off is better as it then lets you do any work on the batteries without fear of arcing, etc.
Take it off, insulate and stick it where it can't come loose and fly into trouble and the draining is killed totally on the coach side.
But this also kills any charging from the RV being plugged in and disconnect on! No coach charging!
Other options are to put a charger on the chassis battery to charge it while leaving the RV plugged with disconnect on and converter charges the coach. Kind of awkward and uses two chargers instead of one?
Depending on how the RV is build for battery location and parts, there may be a way to do it with less equipment?
Since you will have a good charger built into the converter on the newer RV, we can expect it to do a good job of backing off to a good float voltage when the batteries get fully charged.
One way to get less charge equipment needed is to tie the chassis and coach positives together making it one single string of three instead of two and one!
If built side by side, this can be a simple strap from coach positive to chassis positive.
But it appears you have chassis battery in another location, so a strap at the mode solenoid is another possible point.
Click this drawing for best view of a really bad drawing! they did a really good job of making it hard to spot which cable goes where!
But they also do some good with putting tape on the cable ends to help ID them. On a new RV, they may still be there?
The idea with this point is that the mode solenoid is the gizmo which connects coach and chassis batteries together when we drive as a way to get a bit of charge back into any run down coach!
It also connects them when we push a dash switch named different things on different years! Boost, aux, etc are different names they have used. This switch lets us do a "jump start" when the chassis battery is weak!
Since it connects the two together at those times, we can also use that point if we want to connect them to let the one converter/charger keep both charged when stored!
A simple strap between them that is heavy enough to carry any current expected with a switch to connect/disconnect would be my choice. A simple 15 amp rated toggle might be my choice if both battery sets were not at radical different voltages.
There IS a definite downside to this if we are not alert, so consider how you operate?
IF this strap is left on while boondocking and you run long enough to let the coach go flat, you WILL have trouble starting because both coach and chassis will go down at the same rate and you WILL NOT have backup "boost" starting!
But if you have a set process of getting ready to travel and turn this switch off, things will then be just like normal!
New charger to keep the chassis charged or new strap and switch? You likely have to remember to do something to get ready for taking it out of storage!
I DO NOT recommend this for older RV that do not have the much improved chargers built into the converter as they tend to overcharge and run batteries too hot! Either is something to watch for a bit when first doing it, just to make sure you are not charging too hot!
When dealing with a 2015 that seemed a bit too hot, I found a timer on the AC to let it power up for three hours each seven days was good.
Options? Lots of them!
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