The two big players are Webasto and Eberspacher, although there are Chineese makes for a lot less £££.
They will use diesel or petrol, but are not dual fuel, and if buying used make certain it's 12v not 24v.
There is the option to fit a small diesel tank somewhere just to supply the heater, and you could use red diesel in that, but running from the main tank is likely easier and less chance of forgetting to fill up or fuel going bad in the tank.
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