I have a 2016 Thor Ace 294 and plan on putting a 100 watt solar panel on the roof to keep the batteries topped up during the off season when it is in the storage yard and not being used. I plan on mounting it next to the fridge vent cap and running the wires down the vent shaft. I can see the wires from the fridge in the cabinet underneath the fridge but that space is full of heating ducts and the propane furnace. Has anyone else run the wiring this way? If so, how did you get from this area to the battery compartment on the opposite side of the motorhome.
My recommendation, based on your floorplan (fridge on driver's side, house batteries on passenger side):
1) run wire down fridge vent as planned
2) then run wires all the way down thru floor (all you need is a small 1/4"-3/8" hole to run wires thru)
3) once thru floor (caulk hole with silicone on inside and underside), run across rig, place wire-loom over bare wires, fasten with zip-ties
4) go back up thru floor to the location where you desire the solar controller. I assume at or near your entrance door (don't caulk hole until after #5)
5) then your final wire runs from controller to battery compartment by going back down thru the same hole as #4 (again with wire-loom and zip-ties)
6) then caulk hole with silicone
For this long run...I would use a minimum #10 gauge wire, maybe even #8 if plans are to add more panels in the future
One last thing, for this mod...100 watt solar panels cost just $100, so I would install two 100 watt panels on your roof or one large 175-200 watt since you are going to all the time & trouble to do this.
The increased wattage will add value and provide more use for you when boon-docking (since your fridge is elec/propane, not an electric only residential)