Try Walmart, they have fast drying gray primer for 97cents, rustoleum for about 2.50, and denatured alcohol by the quart for under 3 bucks.

Spray your box with primer this morning, give it two coats of rustoleum tonight and then leave it in your furnace room next to the flue so all the fumes are drawn up the chimney, for about a week so it cures out really hard. Then do the fuel proofing bit friday night and you are ready to fly saturday morning.

Have fun.