I like that isolator, have not seen one of those before.
How long are you planning on sitting without the motor running? My goose neck will go a couple days without charging running the fridge and TV/stereo/ water pump/lights. It has 2 12V deepcycle batteries. The problem with it is the genie uses the house batts to start and if you run it to low you have to hook up the truck to charge it up a little. Have a charging line through the whip. MAkes for fully charged batt's when you show up.......
Thinking of adding a starting batt for the genie, that isolator looks like the right one for adding another batt. I hate the diode ones.