St Mary's is like 100 yds from Florida
... Freezing temps are rare, and never for more than a few days. Not enough to worry about freezing a "charged" battery. Lots of time on the hook in Chucktown and Savannah and never had a problem with freezing batteries. Not even here on the Chesapeake with a proper charge.
I might suggest moving up in the wattage on the panel however. Not because your calculations are incorrect, but rather because the economics of scale means the lower the panel wattage, the higher the cost per watt.
For example, because I am limited on space to mount a permanent panel, I had to go with a 100W unit at about $2.00 / watt. If I had room, I could get a panel with almost twice the output for the same price
Controllers are cheap
if you are not looking for the latest high tech, sexy, I got the most expensive, etc... With the 100W panel I added a 30A controller (simple PWM) with digital readout for 50 bucks. Oversized for future expansion and from the US panel manufacturer, not an overseas knockoff.
Think about it... a few extra bucks now, might pay off in less shore power
time or generator
time down the road as well as take care of your immediate needs...
If you happen to want the specs and supplier for the above referenced system, drop me a PM... Don't want to be accused of touting a supplier.