In this next photo, I've removed the wood and found a very filthy two-level battery-holding area. The previous owner had filled these depressions with 2 x 6s and then covered the whole thing with plywood, presumably to get everything on the same level. I haven't checked whether or not the old Group 27 batteries will fit in these depressions but they look like they would. If so, the only reason I can see for raising the batteries is because the battery tray/hold-downs that he was using would definitely NOT fit. But, seems to me the depressions preclude the need for spill trays and it only remains to rig up a tie-down of some sort.
In this final photo, you can see I've cleaned the area up (including the inside of the hull). The 2 Trojan T-105 6 volt golf cart batteries fit in with room to spare. And it looks to me like there is plenty of room aft for 2 group 27 starting batteries. The Trojans, at 225 amp-hours, are half of my house bank. The other half is located under the bottom step at the bottom of the companionway ladder.
For the uninformed, the "house bank" is the bank of batteries that are used for lights, radio, refrigerator, watermaker, etc. Everything EXCEPT starting the engine. The "starting bank" is, of course, dedicated to engine starting. The two functions require different types of batteries. In a pinch, I can flip a switch and use the house bank to get the engine started if the starting bank has run down for some reason.
Tomorrow I'll try to get all the wiring done. For tonight, I have no 12V system. I still have shore power (120 Volts AC) but about the only thing it will run tonight is the charger for my laptop and phone, and the space heater. So, I'll still be able to watch a DVD or two. For lights tonight, I'll be basking under the romantic glow of kerosene lamps. The heat they give off will be nice, too since it's been pretty cold here at night. Beautiful days except for the fact that the wind has just been howling through the marina pretty much all day today and yesterday.