No, not to the shell, per se. I looked around at what others had done, thought about a roof unit, thought about mounting it inside a cabinet with a grill for exhaust. Roof is too heavy and needs support from inside but also most units are about 3x too powerful for the space. Considered a portable unit, but with space at a premium, inside a cabinet was leading idea - but not what I did.
I found a small unit, 5000BTU energy-efficient and carefully measured physical size. Paid a bit more to get a programmable one with remote, which gives the advantage of retaining its settings after power disconnect.
I removed one side of the rear windows
and mounted the unit through the window, creating a bit of a wooden sill or shelf for it to sit on, not too wide. Filled in the remaining part of the window with wood and then caulked it up to seal everything for water and dust. On the outside, I screwed 2 pieces of aluminum in a T shape under the AC unit and down the the bumper (actually to the spare tire mount I added on mine). This is primarily to keep it from rocking while in transit, as it's fairly balanced where it's designed to sit through the window. Unit is intentionally sloped outward a little so it's not quite level - I then drilled 2 small drainage holes in the bottom of the AC unit - in a permanent install, the water is intended to sit there and evaporate, but I found it could leak to the inside if there was still water there when you hook up for transport.
The unit is pretty light
for an AC unit, but it does sit on the shell, in a way... but it does so in the same way that the front bunk is attached to the shell, by mounting it to the wood window trim. The outside windows
are screwed through the fibreglass, pinching it against the wood frames, so the weight
is actually spread out and not just resting on a couple of screws.
Sorry I don't have photos atm - I'd go snap a few, but it's all under snow right now! Hopefully the description helps.