I was going to do something similar to my camper van, right after I bought it, except I was going to put the a/c in the back of the 2' high fiberglass bubble above the rear doors. I even went out and bought a generator, and built a box on the left rear door to hold it.
All good to go.
Then, after actually using the camper for a while...decided I didn't need the a/c after all. With all the windows it has, a few fans have gotten me by. The last two summers, I look at that space again and start pricing out a/c units...and then still don't do it.
And every August, during some heat wave - I swear that next year for sure I'll do it. And then it cools off, and I forget about it till next year.
Current: 76 E-250, bubble-top, self-contained|couple of old Yamaha enduros
Previous wheelers: 41 Willys|78 FJ40|78 Bronco|84 Bronco|74 Ramcharger|78 Ramcharger|79 D150 PowerWagon|77 D100|79 D400 dually, converted to 4WD, utility bed, 10' Lance|75 Westy|69 Scout, RHD|bunch of others|bunch of bikes|couple of boats|couple of motorhomes|blah blah|so what|not my idea|just doin' what I'm told|wank wank|this space for rent|candy is dandy|but liquor is quicker