[Riwright]

I can't answer all of your questions but I'll tell you what I know.

The AC unit sits on top of a large foam gasket. There are bolts that needed to be tightened periodically. If you get a manual for your unit it will tell you how to do it. Take the plastic cover off and you should be able locate the bolts using the diagrams in the manual. You should also see the foam gasket. This is the most common source of leaks that come when it rains.

The manual will tell you how far you should compress the gasket. You should not tighten the screws all the way, that will compress the gasket too much.

However I imagine that if an older gasket is compressed to a proper thickness and still leaking that the right thing to do would be to compress it a little more (ior replace it.)

You can also replace this gasket if that doesn't work. They don't cost much but I imagine it takes a bit of doing to replace it. The installation is simple but the unit is fairly heavy. The manual lists mine at 83.8 lbs.

The manual will give you installation instructions. These should include the size of hole needed for the unit. I believe that the hole sizes are fairly standard. My manual specifies a 14" to 15" square hole. Any unit that fits in that hole size should work.

I don't think that the AC unit has anything Trailmanor-specific in it.