When I weighed 370lbs, I carried a G17 in a Minotaur/Comp-Tac Mtac, with a thebeltman.net belt, all held up by some Perry suspenders.
Basic guidelines apply, regardless of weight: the holster holds the gun. The belt holds the holster. At extreme weights, you add: the suspenders hold the belt.
At that weight, I didn't have enough of a waist for my belt to stay in place - ergo the Perry suspenders.
I regularly wore a t-shirt with an unbuttoned Aloha shirt over it. Tucked the t-shirt in, with the suspenders over it, and the Aloha shirt over everything.
Hid everything nicely.
Now that I'm down to a healthy weight, I carry exactly the same way, minus the suspenders.
If your waist size is, oh, over about 44, I recommend getting a stiffening insert in your belt.