Think of them as a window unit.....
I hate them because out here the plastic tops dry up and if you look at them wrong they break! And walking on a travel trailer roof is fun in it's self. Do enough of those and you start to like trailers... (LOL)
The main thing I found is to keep the coils clean ( Like normal) and they work OK... I try not to put gauge's on them because you'll pull the entire charge out if your hoses are to long.
Good Luck,
Yuma,
What is snow? Is it that white stuff in a freezer?