I can't remember having a icing problem but on real hot days when the AC felt over worked it would stop blowing cold air. I was running it on High. Running lower seemed to work on that particular situation.
I found that one AC was just not enough So I added a second AC to the garage. Lucky for me my unit came as 50amp and prewired for the second AC... That said before I added the second roof AC I used a portable AC in the garage. I vented the 4" ac duct through the lower flip air vent in the garage. I used a plastic rubber maid box that just fit over the vent, mounted it to the vent then cut it out for the 4" exhaust. You would need to plug this AC in seperate to the power pedestal and not to the RV.. May work for you if you have 30amp setup and can't add a second roof AC...