This is just one guy's guess, but it seems to me that as long as you ran the wiring through the ceiling and had a good seal between the speaker flange and the ceiling you should be OK.
I'm assuming that the existing structure would keep rain/snow/etc.. off the speakers.
M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8