We did the same thing in our '69 Airstream Trade Wind.
We traded our Range for a 3 burner slide in cooktop at RV Doctor George
in Sacramento, CA. The best thing about the cooktop is the front burner is a high BTU unit, it will boil water at high altitude. We even got a folding cover for it making for a flat counter top.
That place is fun to browse. They have new and used stuff.
While I was there I spotted a new 46 gal holding tank that I'm going to install under the Trade Wind.
The cook top was the same width as the range so it slid right in but its about an inch short leaving a gap at the back. No problem I'll just make a filler panel out of sheet metal like the ones used in home installations.
I'll move the stile up and make a new cabinet door.