I'm debating my next brew being with grains as opposed to my first two extract brews. The largest pot I have is 5.5 gallons. I do have a cooler I could convert to a mash tun. Which route would you go? BIAB or the cooler? If I go BIAB, I figure I would be making 2.5 gallon batches or so, correct? Would the cooler allow more?