How big of a solar panel do I need?

[DMurdock]

I want to maintain my batteries in storage (this is NOT for boondocking). I disconnect the house (4x6v) and then gen (1x12v) so the only loss is what happens when they are just "sitting there".

Here's how I plan on wiring it (45w panel is just a guess but you get the idea).

FYI - the panel will not be mounted on the bird (mounted on the roof of storage barn once I get it finished)..

I plan on tapping into the charging lines next to the xantrex and installing quick disconnects. If any of this looks fishy let me know...I'm an electrical amateur

thanks!