solar for float charge over the winter

[Helbent]

I will be putting my new to me boat on the hard for the winter in a week. Considering the largest boat I owned before was a Catalina 22, many things about the winterizing process are a bit mysterious to me. That I will be away from the boat for three months just adds to my anxiety.

I have a bank of 2 8G batteries, giving me, I think, just over 500 amps. Calculating a .3% float need, it seems I should have the batteries on a 15-25 watt panel over the winter. I also believe I can wire that panel directly to the batteries without a controller.

Am I correct in these calculations and assumptions? Any additional advice?

Fwiw, the boat will be stored in St Marys, Georgia.