Wow! I am sure confused, you replaced an RV battery? Golf cart? 6 Volt?
The chassis battery is what needs to be looked at, what is the voltage currently? Check it with a multimeter. If you need to jump start, after it starts, check with a multimeter again. Is it charging off the alternator/ generator?
You need a strong starting battery for the engine, not a deep cycle battery , the golf cart batteries (6 V) are for running the interior components, if you are not plugged in to shore power. And when you are plugged in, do you have a built in charger? Is it working?
I don't mean to confuse, but I am not sure if this can be what you mean.