'My purpose for adding a solar panel is to maintain the battery while in storage'
maintainer poor choice/poor value/poor performance
Get a controller like
http://www.homedepot.com/p/Grape-Solar-40-Amp-PWM-Solar-Charge-Controller-with-Bluetooth-GS-PWM-40BT/207100856tap into the existing wire, and add a panel
http://www.homedepot.com/p/Grape-Solar-100-Watt-Polycrystalline-Solar-Panel-for-RV-s-Boats-and-12-Volt-Systems-GS-Star-100W/204211365cut the ends off the panel wires, add as much 12g landscpae wire (by the foot from orange big box) as needed and the plug, <$200.
get the app from grape and monitor via bluethooth 'round the campfire!