I know that others have made them like this, and I admit that I used some ideas, but I wanted to show mine off too.
I cut the top out with a jigsaw and then cleaned it up with a dremel. The lid was hollow so I used spray foam to insulate.
Finally I spray painted some hose clamps white to match the lid, drilled holes in the rear of the cooler, and mounted the clamps with stainless steel bolts/nuts and used o rings to maintain the seal. Then I clamped a 9 oz. paintball tank and regulator on the back and hooked it all up. Good to go.
Thanks to everyone here that I stole ideas from and I hope that this helps others create something as awesome. This is my new best friend on camping trips!