Our last caravan (Fleurette Tamaris) didn't have heating.
We used to use a portable fan heater with thermostat that we bought from Aldi for £10. Worked a treat.
Our new van has a Thruma heater which, like you, I struggle to regulate. I find that even on the lowest setting the van gets unbearably hot and I end up having to get up in the middle of the night to switch it off.
When we had Truma blown air heating before going to bed we changed it to the lowest setting ie 1Kw and turned down the thermostat, also switch off the blown air. It helped but you still end up with hot and cold zones. We bought a cheap oil filled radiator type heater. Found the cheap fan heater made too much noise when it switch off and on.
We now have Truma wet heating and it is awesome, no cold spots, not hot spots just even heating.
We use a cheap convector heater with thermostatic control. We have paid for EHU so why not use it. Only ever have it on its lowest setting though, and it keeps the van nice and cosy.
Either an oil-filled rad, or a convector heater would do. They are both silent and have no exposed elements. A fan heater would heat it up quicker, but they are too noisy to leave switched on, especially overnight if that's what you wanted. A slight advantage with a convector heater is that they tend to be a bit lighter, but unless you are really on your weight limit it would make very little difference. We just went with what was cheap and convenient.
I fitted a wall mounted convector heater in my toilet/shower room. It has a thermostat and if we leave the door a little bit open heats the whole van slightly. I originally fitted it as it is nicer to have a shower in a warm room.
------------- We camped for years. In 2019 we bought an Elddis Avante 454. We like it as it is short (6.9m) and fits in our driveway and has a fixed bed.
We had 127 nights away in the caravan in 2023.