OH I was thinking a tray inside an compartment.
What I did on my OFF-ROAD POPUP trailer is mounted some right angle sections that extend out over the trailer tongue. I was extended out on both sides of the tongue and was able to line up four 12VDC batteries end to end... I did not have a height problem. I actually picked up four each of the plastic battery boxes from WALMART and mount ed them first then just set the batteries down inside the boxes. Then I added the snap in place lids...
This is photo of three batteries mounted end to end between my propane tanks and the trailer deck...
After adding the angle strips that extend out on both sides of the OEM mount I now have four 12VDC battery boxes mounted end to end..
Also TORKLIFT makes a battery hanger you use for one battery mounted under the trailer to the main frame under the trailer..
Another solution might be mounting one of these 48-inch SIDE-MOUNT TOOL boxes (PEPBOYS) and you can mount four each T105's end to end inside this box. This is better idea keeping the batteries more safe from being stolen when left unattended...
You can mount BLUE SEA HD Battery switches and battery vents on the inside of this box as well...
Roy Ken