This has to be in the forum somewhere but I wasn't seeing exactly what I'm looking for. I need to make an extruded cut through this barrel such as that shown. I know what the distances from the top and front planes need to be to get the opening required. What I don't know is how to create the sketch so that when the cuts are projected on the surface they are where they should be.

This the cooking chamber for a smoker, eventually the part cut out will be replaced with material to serve as the door. Maybe this could be done all in one step by cut-extrude only an 1/8" all around and then creating a new part from the "door" that is left?