I'd stay away from that for mashing for 2 reasons. The first being the amount of head space you'll have when you mash is going to make temp control a nightmare. Second from what you are describing it doesn't sound like its insulated, which is one of the main reasons converting a cooler to an MLT is so regularly done. Just my two pennies.
Primary-Lemon Lime Wheat, American Hopped wheat (galaxy, Amarillo). Classic Porter, Kiwi Lambic.
Secondary-Sour Brown Ale
Bottled:Belgian Tripel 3/20/10,Pumpkin Pie Milk Stout,
Kegged:West Coast style DIPA