Jumpstart from auxiliary battery

I think what OP is referring to is the fact that current from both batteries is (by definition) available at the battery isolator. You can use a single jumper cable (and often even just the clip) to connect those two terminals together. This does the same thing as the "boost" button that some rigs have. You can also, in many cases, provide a circuit between one of those terminals and the "engine running" signal that often controls the isolator. The advantage of the latter is that it is a low-current circuit, so you don't even need jumper cables.

Beware, though, that many manufacturers cheap-out on the engine-to-house wiring, so it may be better to just let the battery charge a bit rather than trying to directly start with the isolator defeated.

Sorry, but I don't know anything a bout RT specifically.