It is easier than the first reply suggests
First.. If you do NOT have a driver's door here is what i did
I took a 2x4 beveled one edge a bit to make it look better, Stained it to approximate the primary interior color and bolted it to the wall next to the driver's seat... I will discoss other options in a bit.
I bolted brackets to this. Ran 10ga wire from teh batteries to a Rig-Runner power strip (Uses anderson power poles you do not need to do this) and mounted 3 2-way radios on the 2x4 along with other stuff.. Two CB's and a 50 watt ham rig.
Only issue I had was with condensation from teh window if you do that I'd suggest a drip guard (Silicon cutting sheet between bracket and 2x4 draped over radio to block drips (Cost me one radio)
For the antenna I ran the coax up and out the "A" pillar (The first pillar) and set a bracket so my NO GROUND PLANE antenna tip was about 1" higher than the highest point on the RV (Automatic "Bridge Stick")
ALternate point
The center "Pillar" on my Damon (Center of the dash between the seats) was just a plastic panel.
You can easily mount rails behind it and cut a hole for the radio and frame the hole so it looks good. Or mount the radio on it (I would put rails behind it to add support.. Rails are upright brackets bolted to the floor like an audio Rack Panel)
Oh the coax to the antenna
The hole I drilled was directly behind the bracket. Brought the coax out and atteaced the end (Connector) then filled the hole with GOOP (Adheasive sealant) to keep that which needs to be kept out... out.. then slapped the bracket over it and lagged it to the RV.
The bracket was half a mirror mount.