The problem I'm having is that there's a location I need to use for a 5000 BTU A/C unit, and I'm having trouble figuring out how to do the installation without future problems, with air & water leakage, bug infiltration & a tracking system. I'm sort of stuck with the front-mounted location because of weight distribution (battery, ice chest & stove in the galley). I need the weight of the steel tongue box, storage & A/C unit as a counter-balance to the galley weight.
The A/C unit will be located in the headboard area, above the existing tongue box (box is 22" tall). Here's a picture of how it will look, imagine a unit sitting just above the tongue box. The side panel has a block at about the the height of the A/C shelf, but notice how narrow the actual shelf will be, about 7 1/2" deep, front to back.

The A/C unit itself is about 14 1/2" deep (front to back), so the "stowed for travel" position will actually be slid into the sleeping area about 6"-7" and for use, it will have to track forward that same amount so it isn't a head-knocker. The "front" of the unit will slide over the tongue box lid for naps & sleeping at night, it must have a drip system for condensation, clearance for the airflow to outside air for the heat exchange, and be sealed up when traveling. Don't want any leaks from air, water, driven rain or dust from dirt roads while pulling.
I'm having trouble wrapping my head around all of this and have been pondering a solution. I can picture an outside cover which hinges at the top to act as a sealed box for travel (I've seen that one before), but the tracking, water drip for condensation, seals & water proofing for actual use are what's keeping me confused. If it's running & there's a rain storm at night, what then? It's the proverbial 10# of you-know-what in a 5# bag. Your input is valued on this one. Pictures for solutions would be most helpful. Thanks for your replies, tim