Algae will only grow if there's water in the fuel--so keeping water (including condensation) out is the main thing. You'll mostly get condensation if there's a vent to the tank--you can cover the vent with tape if the tank doesn't heat up and cool too much.

You can also add a biocide (like Bio-Bor, available at most marinas or marine stores: www.westmarine.com). That'll kill algae and keep it from growing.