From your limited use get 2 flooded GC batteries which are deep cycle. Buy a box big enough to hold both. I bought a box that was easy to seal for my son, plus 2x Interstate GC's. We cut out the vents from his old box and used them on the new box. JB Weld glues almost anything forever.
12V batteries are NOT deep cycle except for a few very expensive ones. "Marine Deep Cycle" are only slightly better than starting batteries.
There are 6V AGM deep cycle batteries like my Lifelines and the absorb/bulk voltage is 14.4V. Normally they don't vent and if they do it's the end of the battery.
My toad has a 12V AGM starting battery that is completely enclosed and you attach a small vent line to it. That's because it's inside the car under the passenger seat. I'm not aware of any similar vented deep cycle AGM's.