I think you definitely want to enclose them for 2 good reasons. First being safety since if a metal object gets across those posts it will be very interesting to say the least. Second would be to minimize temperate fluctuations. I also think getting them up off of the floor is good to help prevent a big temperature difference in the top and the bottom of the battery. Sitting on a concrete floor, for instance, will suck heat from the bottom of the battery.

I say nice score on the batteries if they are still near spec.

Cheers.

TomW

The Truth is the Truth, even if no one believes it; and a lie is a lie even if everyone believes it

Yours are packaged pretty good the way the are, you only need a box to protect them from stuff (metal !) falling on them and to be able to vent gases to the outside (those gases are explosive). Both of those are safety issues.

The simplest I can think of is a plywood box just a little larger than your batteries, with tbe bottom part reinforced by some 2x4's or so in case you want to move the box as a whole.

The lid should have a vent in it, with a tube that allows gas to go outside of the storage room (and out of the building) to avoid dangerous concentrations of gas during heavy charging.

Temperature is an issue, but it is more of an issue when the batteries are discharged, so keep an eye on charge state when it's cold, with a normal charge/disharge cycle when it's cold around the batteries a simple foam insulation layer on your box (maybe make it double walled) should keep thm well even when it is -30 celsius or so.

 It will be simpler and much more relivant to use voltage to turn your vent fan on and off as gassing is voltage dependant. Many inverters have programable voltage controlled relays within them that could be utilized for this,Xantrex SW, Outback. Some of the PV controller co's have small voltage controlled boards to drive relays , also many charge controllers can be configured for this.  There are also purpose built vent fans that operate on this principle.

 I have used blue board under smaller batteries with no problems and your L-16 size batteries should probibly be OK. I don't know what the compressive load limit of the foam is though. I would make sure that the batteries are restrained from tip over, in case the foam starts to crush.

I thought it would be nice to have a good acess to the batterys for maintainence.
I already had the adjustable angle shelf there so I just cut a piece of 3/4" hardwood plywood for a cover. It is hinged and latches in any position. I can cover the foam with plywood but I don't think

 I don't believe the foam I have will crush, it is high density and it had truck tire tracks on it. I have learned the local lumberyard will give you the broken pieces since they can't sell them.

I think I'd have an inch airgap under batteries along with an inch space inbetween cases, with insect screens over foam board vent slots to keep the weevils out; keep the cut out pieces for re-inserting for the bitter part of winter. Hard to rodent proof foam, here in Minnesota the white-footed deer mouse will nest anywhere there is a hint of warmth - I've seen foil burger wrappers shredded in their nests more then once.