Simple job but takes some care as you will be working with both the start battery as well as the coach and both of them are fine, IF you do some things to make it safe.
So first, do make sure you actually need to replace the solenoid. Have you checked that it is not actually passing current or is it possible there is a dirty cable not letting the voltage get from the solenoid to the coach batteries? There are often big "mega-fuses" inline which can get corroded and open the path.
I recommend checking for that before going to all the trouble to get to the solenoid.
First job will be the trick of getting space to work and that often requires taking the breaker panel loose to lay it aside, so first step is to make sure there is no chance of dropping or doing something to make a big arc! That can make a small job great big!!
But if really needing a new solenoid, take the negative battery cables off both coach and start battery first, then disconnect the AC power cord as a way to assure there is not power from inverter or converter in the space.
Pull anything like the breakers out of the way, then take a look at the cable markings to match up with this code.
There should be marking along the wire sides of the small wires:
FM is the ground wire and attached to the mounting screw, LR is the signal from the dash area to make the solenoid work.
Then there are tape markers added to the battery cables as this code:
This is a snip of your RV solenoid:
Click this picture to get a betterview.
Look first t make sure you can tell which wire goes where to go back and it is pretty simple from there.
Getting the power off everything and being prepped makes it safe. Taking a picture first is one way to help put it back right but if the markers are stilll on, it is not bad either way. !