Just keep in mind that INVERTERS are very DC POWER hungry. A 400WATT PSW Inverter could draw as much a 35 or more DC AMPS from your 12VDC battery. I think you are saying this would be your truck start battery with your NO BATTERY BANK statement.
Rule number one in my case is 'NEVER EVER' mess with truck start battery system. This is how we get home hehe...
What you want is a CAMPER battery setup that is kept charged up by an on-board converter/charger unit. The shore power connection will keep this battery all charged up for you...
When you are off the power grid then you have to have enough battery power to run the things you want to be using from your CAMPER BATTERY and then also have a way to re-charge this system like using a 2KW Honda type generator a few hours each day when allowed to run a generator.
As usual adding one thing always requires something else to work right...
Looking at what you have installed already you are almost to the standard items for a 30AMP trailer system
Just things to think about...
Roy Ken
