
So, here we are:
1.) Heater box under van. Rough and ready I know but that's all it needs. I'll underseal it before the winter. Pipes and wires, left to right, are air intake, fuel line, burner exhaust, 12 volts supply (I see it needs me to sleeve it properly), and at the far right the hot air outlet duct:

2.) Hot air duct inside cupboard, as described:

3.) Hot air outlet, closed. Not discharging directly into the sliding door footwell as I said but able to be directed into there when the bed is down above the outlet - as shown in picture 4.

4.) Hot air oulet, open and directed out into the sliding door footwell:

5.) On/off switch and room thermostat.

Hope that helps.
I suppose you could branch and extend the hot air up to the AFT vent, to keep a child warm - good idea, as long as you've also got a thermostatic control up in there! Remember though that the standard ducting gets hot, so it would need to be a bulky well-lagged bit of pipe. I also suppose that, in a less cluttered unconverted Bongo, you could probably make that a semi-permanent rig. If you do it, would much like to see the result, as it could be a good move for upper floor sleeping generally.
(I wouldn't be so indelicate as to tell the forum who snores in our connubial bed. Anyway, I would get banished to lie under the Bongo permanently

Cheers, David