The battery box should be sealed at the bottom. One of the intents of the box is to retain the acid should the battery leak or boil over. By drilling holes in the bottom you may well be setting yourself up for acid damage to the trailer. Small chance but is it worth it?
Find how the water is getting in and fix that.
Chuck - Sparta, TN
2012 Jay Flight 22FB, 2 x Honda EU2000i
2013 GMC Yukon XL Denali AWD
EDUCATION is what you get when you read the fine print.....
EXPERIENCE is what you get when you don't.