Tony,
Yes, it is normal and it is a good idea for both RVs and boats. (Which are also R Vessels.)
There should be nothing on the main engine (chassis) battery that is not directly related to the main engine. The house/hotel (coach) can do what ever you/it wants.
If the house battery goes down, you get dark and maybe cold.
If the main engine battery goes down and you need the engine, that could be a very bad situation.
Most RVs (both types) charge both battery banks with the main engine. So, you have a built-in redundancy.
Before the depression, I did a lot of electrical work on boats. While many smaller boats had a single bank, I was frequently hired to make the system like this after the owner got towed into port.
Matt
