Do a search of the threads related to this, particularly the pushbutton ACC unit and somewhere within those many threads there is a discussion that mentions the amperage that the control unit is rated for.
If I recall correctly it was mentioned that the controlling circuit and component is maximum rated at 1.2 Amps.
So in order to protect the electronics you would need a fuse rated to blow below that rate!
A 1 Amp slow blow in a waterproof in line holder placed into the power feed circuit from the would seem to fit the bill nicely.
Good Luck!