WHAT I DO, NOT NECESSARILY A RECOMMENDATION FOR WHAT YOU SHOULD DO:
I have my two big (Group 31) "wet-cell", aka "flooded" (i.e., potentially H2-venting) batteries in the storage space under the passenger-side couch in my FWC Hawk, next to the front turnbuckle-access port. I keep that turnbuckle access port permanently open about an inch as a vent to the truck-bed/outside. I don't know if even that small amount of venting is necessary, but I see no downside to doing it, so I do.
My camper has never exploded or burned in over 5 years running that way....
...Because, as D.R. said, H2 dissipates much faster than a fart.
BTW: AGM and Gel batteries are also lead-acid...if you want to talk about the other-than-AGM-or-Gel type, call it "flooded" or "wet".