Just take the covers off the back of them for a couple of dry days and let them air out. Taking them all apart and resealing them might not work anways, there could be a hairline crack you can’t see or they could just have poor ventilation in the first place. After all these ARE ebay lights.
And what’s so wrong with drilling a small hole in the bottom? As long as you do it on the back side and use a really small bit like 1/16" or smaller, it’s not going to harm anything.