I ended up cutting a rectangular hole as I don't have anything other than an angle grinder that will cut stainless steel, so I marked out the location, drilled 4 holes, one in each corner of the rectangle and then did the cuts, it came out pretty good after a little cleaning up of sharp edges with a file, then it was a matter of locating the heater selecter over the hole, back drilling, appling silastic and bolting into place.
