It seems like swapping out a Truma Trumatic with a diesel heater could work, but it depends on the available space and whether the new heater will fit. You might want to check out Chinese clones or other affordable diesel heaters, but make sure to research installation needs carefully.
Here's a link to a Chinese clone diesel heater
https://www.amazon.com/12V-Diesel-Air-Heater-Caravan/dp/B08ZK3JN2L