Maxx, lube the bejezus out of the gasket with either silicone or teflon based lube! When you go to tighten the bolts tighten north then south then east then west to put even pressure on the gasket, you can then tighten the rest in any order.

Depending on how old the unit is, you'll need either 2 7/16" wrenches or a 7/16 and a 3/8" wrench. It's easier to put the bolds in from the bottom so that you have better access to the nuts when tightening them