We've always had ovens and don't prefer the cooktops. However, most coaches on the lot have just the cooktop. When we were shopping around we asked about swapping it out but the dealers didn't want to do that, which is one of the reasons we ordered our coaches.
The mechanical end of it is no big deal but they didn't want to mess with the cabinetry. If someone was real good with woodworking it might not be that hard to do. The wiring and gas line isn't that hard but it would probably depend upon how the cooktop and oven differ as far as fitting into the solid surface countertop neatly without turning it into a hack job.