This tank is 30 gallons.
Its the B162 tank, 30x24x10. the 30" is the length and it could be longer to get more capacity. I would not got any deeper or wider. It fits lit a glove now, longer than 24" will not fit on to of the "vee".
As you can see there is a slight offset of the hall, so the tank looks ~12" off center of the floor, this gave me enough space to ease it in. (Notice the foot prints on the tank LOL.)
You may be able to get about 6" more easily. There are a lot of configurations available. You can always go long and skinny but you have to consider the working spaces around.
My house bank is located on the port side of the port engine. Its a pain to get too but its a nice spot. Plenty of room for 4 batteries. My Starting Bank is forward of the port engine.
Here is a thread on the tanks.
You have to hold your mouth just right to get it in, but its relatively simple once one do it about 3-4 times.
I bought the tank from RONCO PLASTICS.