@ BFL13: So an ammeter would need to be installed in the system to adequately monitor full charge of an AGM. Not a huge deal but another item to consider and install. I assume the charger is not able to measure and sense this because there is no programming for bank capacity (in Ah). Sounds like a nice feature to add to them.
@MEXICOWANDERER: The battery cases are 12.25" long inside so a 27/31 will not fit. Recall the battery(ies) are in an enclosed compartment in the rear of the trailer not out on the tongue. So they must be in vented cases. I have mounted a battery cutoff and digital voltage meter through the front of the existing case and the GP24 just fits.
As for the battery vs. tire debate. If I run out of power I can fire up the generator, start the truck, or turn on an LED lantern. If I blow a tire I can tear up my rig and be stranded who knows where.
For sure we agree on purchasing quality tools. NO debate here! HAHA
Decisions for me are about value. The best and most expensive is not always the best value.
And yes a top quality AGM is expensive and may outlive my rig (and maybe me). I cannot justify with 1-2 weeks boon docking a year.