At the moment, weather permitting I'm fitting a heater into the hybrid, no heating at all
Blue toes and fingers
When I was doing minibus work, some of the bigger units had heaters in the back of the motor under the seat. They were basically small car heater matrix's, in a box with long pipes from the engine to circulate round it, with a small fan unit to blow out
I took one out before scrapping one. Re done it up and have at the mo got as far as sitting it into the cab, and running two pipes from the engine in to it, ran it up on the engine and got the heat curculating through the matrix, all I have to do now is run some electric to it to run the fan
The thing is you can find these units in allsorts of vehicles, old crew cab trucks, like british rail etc, if they are fed from the vehicle heating system no probs
Or make a box up, get a small fan unit and matrix and make your own.
At a push you could incorporate a small heater unit from a car itself complete, you may loose the middle seat, but would be worth it.
Here's a pic, the unit when I finally fit it wont show the pipes and fittings, they will be under the seat box