Hi,
I put a canvas tarp on the roof and that prevented any holes into the roofing material. You can use cardboard - even the box it comes in. A pickup next to the RV can mean that you only need to lift it from 5' off the ground to the 11' tall roof, so it can make it easier. I had a ladder rack on my pickup with a extension ladder on it, that was nearly 6' off the ground, so it was really easy.
Most air conditioners are the standard size, for 14" square openers. You do not have to stay with the same brand or BTU capacity.
I would stick with a ducted unit, they are so much more quiet.
Fred.