There is NO good reason to remove batteries unless maybe you have no access to power to keep them charged. A fully charged battery won't freeze until something below -40F and the cold is actually good for them.
You will get better answers if you post the make and model of the converter/charger in your RV. Some will float the batteries properly and some won't.
If you insist on starting your engines periodically, you need to run them until HOT......not just warm.
If your storage period is 4 months or less you should be able to fully charge all batteries, disconnect the negative cables and just let them sit. If they don't survive that, they were bad to start with.
Same for the engines. Stabilizer in the gas and leave them alone.
