I have 3 lights and a 12v fan above my heater in my 6x12 shack. I run it off of a flasher battery with an inline 3 or 5 (not sure)amp fuse. I can run the fan for a full day of fishing while using the lights in the morning in the dark for alittle while. I used to run a normal 12v deep cycle but found it was just easier to use an extra flasher battery. Its nice to have the xtra flasher battery around too incase someones goes dead, they can use the extra in the flasher. I bought 2 extra flasher batteries so when 1 is charging at home I bring the other to the shack. Its just way easier to deal with for me as U can put a flasher battery in your jacket pocket when you leave.
I still use the large plastic deep cycle battery as the holder for the flasher battery. I made a holder/cut out for the flasher battery out of the pink board insulation. Than I keep extra fuses in it and always have the option to go back to a large 12v deep cycle.