My brines usually have the basic. 2 parts sugar (white and brown or splenda is ya watching your girlish figure) 1 part salt, 1 gallon of H2O.
I heat a measured amount like a quart, then add 1C white, 1C brown, and 3/4C canning salt (It weighs more, finer grind). I get it all in solution then I add in another pitcher, ice and enough water to equal the gallon total (thats 3 qts). Its cooled and its close to the gallon total.
Like Bellevue said the ice chests are usually broken down by quarts. My igloo 48 is 48 qts, the 100 is 100 qts. etc.
You can build the brine as you want it, if you add extra flavor modifiers like herbs, veggies or fruits its best to steep them first to draw out those flavors then cool them before adding to the brine. I usually do all that in one group while dissolving the salt and sugar.
You knew how, you were just testing us...... right?
You'll do fine, don't forget pictures!
Bon Chance