I have a Lund Pro Guide, with a similar if not the same trolling motor battery compartment located below the rod storage area. I run two Wal Mart Everstarts 29 Deep Cycles lead acid. MK 315 charger. I have never loosened or taken the battery compartment off, when charging. I have never had an issue, with that set up. These particular batteries don't seem to off gas much, as I hardly ever have to add water to them. I typically fish 4-5 hours, with the 80# MK usually set on 4.5-5.0. The gauge on the TM base only shows a discharge of about 25%. I have not ever tested the amount of discharge with a more precise meter.
Now, the starting battery goes in a separate compartment, also in the floor. I noticed over the winter it was not holding a charge very long. So upon replacing it earlier this month I noticed I had an issue with some paint bubbling in the compartment, caused from acid from the battery. What really happened I don't know. I replaced that battery with a Duracell AGM, basically on HRG's recommendation. Came to about $198 with tax, and after 10% discount, and $10 rebate:
https://www.batteriesplus.com/produc...ls/sli27magmdc
Sams Club has the same battery cheaper, but I don't have the $45 membership. I looked quite a bit, only two places that I found that carry that Duracall AGM is Sam's & Batteries Plus.
Hope this might help, Gregory