question

No offense but if you don't know how to do it you should ask a local installer for help.

The installation of an Orion isn't that difficult.

+ and - from the starter battery to the input and from the output to the auxiliary battery.

I second Matthias' suggestion to seek professional help with the design and possibly the installation. If you don't know what you are doing the installation could be unsafe. Fusing, wire sizing, etc all need to be considered in the design. This is all discussed in the manual. But again, if this is over your head, get help locally.

All vehicles will involve a battery and an alternator as part of the starter system.

Normally, you'd only want to charge your auxiliary battery when the engine is running to avoid discharging the starter battery. You can wire the remote control to power source that is switched on and off by the ignition switch.

Tthe DC-DC converter you call out has "engine shutdown protection" that automatically detects the alternator state, so wiring the remote connection into your existing electrical system shouldn't be necessary. But it does require setting the threshold voltages.

An "isolator" is a low cost device that provides SOME independence between the starter and auxiliary/house electrical systems. But the Orion solution is far superior and provides much better protection to the house battery and the alternator. The Orion is the "right" solution.