If it was me I would pickup a REAR MIRROR Antenna mount that looks something like this... Used to find them at Radio Shacks but now you can't find Radio Shacks any more. AMAZON will carry them if you can find a part number...
Mount it on passenger side where the door is so you can run the coax through the weather strip on the door.
If you mount it up high on top of the RV you are only going to knock it off going under something. No fun in that just to gain a few more hunder feet of range.
CB RADIO is more or less line of sight using the 27MHZ frequncies and the radiated power is very low wattage... Have no idea what bands CB'er use in Canada - Probably same as US being 27mhz...
Running with a group alot of folks would do just as well using one of the portable CB units with walkie talkie type antenna...
I wouldn't spend alot of monies on your antenna setup. Make it as simple as you can. You can mount on top of the MH and do all those things everyone says to do and all you will possible gain is maybe a few hundred feet more - 1/2 mile at the most... haha...
Having said all of this by nature of the 27MHZ you can work half way around the world when the bands are open. CB frequencies bounce of the atmosphere by multiples of 1500miles as I recall... Locally you would be hard to talk to anyone mobile to mobile as far as a mile away from you. That would be stretching things...
Roy Ken