I do NOT keep my trailer in a garage but it does stay in the shade of a metal awnning.
The first time I polished my trailer it took me approx. 47 hours (and 18 hours by a friend "pitching-in") to polish my trailer completly. Bear in mind that it did not have a clear coat, but the aluminum was highly oxydized, the trailer is a 1958
and had never been polished.
Now I just wash it with soap and water before going camping and wax it once a year ( approx. 5 hours ).
Hope that answers your questions,,,, Good luck in whatever you decide.