you obviously haven't seen many older semi tractors. and I never said it was smart, just that with common sense for 1 day at a meet, and that if done properly it should be fine.
I have 4 non sealed flooded group 78 batteries in the trunk of my 78 z28 "per NHRA rules" with no vents at all and have had them there for over 10 years. no acid marks no spills not a single issue.
batteries that are used daily will vent, but in short duration use if the battery starts venting there is an issue somewhere with the charging system or the batteries themselves. physics are physics dude.