I am another posting Joe Schmo. I have had an AGM inside my TC without venting since 2005. Never had an issue. I would not put it in a sealed container. I believe it is pretty much spelled out in the literature. Most people do not realize that many if not most computer UPS's use AGMs, and they are vented into the room they are placed.
If you ask the manufacture any question, keep in mind the attorney's have their input.
Lots of people confuse gel cell batteries with AGM batteries.
Lifeline says:
"Never install batteries in an airtight or sealed enclosure and make sure installation is adequately ventilated."
Key words, "airtight" and "sealed enclosure".
Wayne