Which is better - (3) 12v batteries vs (2) 6v batteries

Per the Lifeline Manual

Document No. 6-0101 Rev. C Page 22 of 36 wrote:
There are four main safety hazards associated with the use of any valve regulated lead acid
(VRLA) battery. These hazards are: a) Release of ignitable gas, b) Exposure to acid, c)
Shorting of terminals, d) Thermal runaway. This chapter provides a description of each of these
hazards and means to mitigate them.

I see no requirement that precludes me from using AGMs inside my TT or van. I view neither as a sealed or an airtight container
.

Also, there are four APC UPSes in my house and two dead ones in the garage. I pried the top from one of the batteries and found a simple wet battery! These things die because of water loss as there are NO valves at all! That scares me more than the AGM I sleep above in the TT.

HTH;
John