Wallas XC Duo is less than two thousand new from store, it is originally designed for boats but I’ve seen them installed in small campers recently. If you can source older Wallas cooktop from a boat, some of them can be fitted with a fan cover so they will work as a heater like this new one.
I’ll bet installation would be less than 8k, even at the most expensive shop 
Since UK guys are big on small campers, they are marketing it directly to campers too: