Several have done the ultra heat conversion. If you use the search facility you should find some good information.
The more common route is a 500 watt oil filled radiator. This is quiet and up to the job of out of pre and end of season camping, but not winter.
On my Triton 340 I took another route and fitted a shallow Adax 500 watt shallow/panel heater just inside the door as you go in on the left.

Colin

Photo of Adax heater if interested. The socket under the sink is fed from the electrics readily accessible behind a timber partition. I plug a cheap timer into this so the heating is programmed to come on before we get up and evening time.

11 - adax heater-800.jpg - Bild entfernt (keine Rechte)12 - adax heater socket-800.jpg - Bild entfernt (keine Rechte)

Colin

ps, we have 3 of the De Longhi Bambino oil filled 500 watt rads.We use them in that spell before and after winter at home when you don't really want to put the central heating on. Yes other makes are available at 1/2 the price, but they are nicely made, look good and have a 5yr warranty.

Thank you. I wanted something as neat and "factory fit look" as possible. When I bought the radiator it was about £45, but has now been superseeded with it's replacement far more expensive. https://adax-solaire.co.uk/product/adax-...tat-option-2-2/
The front of the rad lines up more or less flush with the door openeing as I was able to mount it through the case on 18mm thick plastic discs and not use the radiator brackets supplied. If you have space for something like this and can buy one at a sensible price it is worth the effort. These electric rads seem to be a northern European thing as they are used opposed to the hot water radiators we have in the UK.

Colin

It should fit and look OK, but I don't think it would be effective. As it is so high up the heat would not have chance to radiate out before it hits the roof area and escapes.

Colin

Nice idea. If not camping in colder weather it would be just the job. I suppose for the occasional time when you would be camping in colder weather then a small ceramic heater could be carried as a back up. I cannot remember seeing a larger output panel heater that would fit in the space.
Instead of going hinged why not make life easy and have it on a fixed plywood panel. To get access to the space behind go through a flap/hatch in the bottom of the wardrobe. All the joinery work is then not on show.

Colin

Just come across next size up from what I fitted, and at 1000w if it would fit make a 3 season heater.
https://www.adax.lt/en/1353-portable-hea...p1110-ktp.htmls

Colin