Battery location

Eric, I've been holding off commenting in the hopes that someone with a Classic could give you the exact location. All I can say is that being very familiar with the Barracuda which is thought to be the same hull is that it is under the front seat. On the Barracuda with a bench seat, a pretty standard battery (group 24) will fit. The Barracuda's with the bucket seats used a battery size with a low height to get a small lid on top covering it up.(it sticks above the floor a couple inches) Since you have a bench seat, I would have to say it would fit under the passenger side of the front bench.

Eric, Excellent direction with the cloth. Some have gotten real fancy with a layer of roving and then cloth but I feel a couple layers of cloth is great. The thickened with cabosil resin will work to fill in any gaps under the new stringers as well as create fillets at the junction to the hull. Gaps under the stringers have also been filled with saturated fiberglass mat by some but if you spend the time to scribe the new wood to the hull you really won't have big gaps.

I think you mentioned that you did read the threads here on stringers. Did you catch the half round cutouts on the bottom of the stringers for draining water to the center of the hull? If you didn't, I'll run through it again.

Glassing in a battery compartment in my opinion is overkill! Originally they probably had a plywood box! I would may a "tray" for the battery and then just give it a couple coats of resin.