Which RV Deep Cycle Batteries To Buy?

I don't have enough trailer experience to get into the 6V vs. 12V debate or recommend a brand. If you get the lead/acid variety, my ag experience tells me that you need to check water levels at least annually and try to keep them trickle charged throughout the year - overcharging with higher amps will heat the battery and drive water out of the cells. What I have found out the hard way about trailers is to make sure that whatever you get will both go into and fit securely in your battery box. Right now, I am using two Exide 105 ah 12V deep cycle batteries from Tractor Supply connected in parallel for 210 total ah when new (they are big and heavy, and I had to modify the battery box to get them to fit), and then found out that Costco has the same size and rating Interstate battery for less. From the little batteries on ATVs, I have learned that the AGM variety is easier to handle (no acid spills), but can't compare longevity or price with lead/acid for trailer use.

JRMunn