20 watt panel

[Shiny16]

I have a 20 watt panel and small waterproof controller. I have no expectations except to maintain two lead acid group 24 batteries while in the storage center.
I was thinking of mounting this on the roof of my sport 16 and using the pre wires down to the dinette and out of the hole that goes to the battery lead. I would then have the waterproof controller on the battery box. The leads from the controller would stay attached to the battery. I would just disconnect the battery ground when in storage. I want to minimize drilling or altering the unit.
Are there any issues with this. Does the solar panel need to be grounded? I'm pretty lacking in electrical knowledge.

Thanks

[Shiny16]

Also would it need a fuse inline?