An update, now it's fitted, which may be useful for anyone considering a Chinese heater. I've fitted a 2KW diesel heater, under the driver's seat on a stainless steel bracket. The heated air is ducted above the exhaust across to under the passenger seat. Fitting was reasonably straightforward, though I've replaced several of the original parts:
There wasn't enough ducting, as the heater is obviously sold to be mounted in the vehicle with no ducting on the air inlet. The air inlet end of the heater (fan end) is slightly larger diameter than the 60mm ducting available, so was a struggle to get on.
The exhaust supplied is not designed to be bent much, or cut. It cracked when I bent it and the internal diameter is only properly 24mm at the ends, so can't be fitted once cut (still on in pic below). Replaced with a metre of Webasto exhaust.
Replaced the main jubilee clips and P clamps.
Bought a proper fuel stand pipe to drill through fuel sender and routed fuel pipe above heat shield, through a length of water hose.
Wrapped the pump and filter in insulation to reduce noise.
Needed an air inlet for the driver's step, as not supplied.
I used a 64mm hole cutter for all cutting - driver's step, under passenger seat and through heat shields above exhaust. Heat wrapped exhaust where it was near the ducting and gorilla taped the edges of the holes cut through the heat shield, as they we are sharp in places.
I cut sections out of the under trays, rather than cutting holes, so they can be removed without removing ducting.
With the upgraded fuel supply, ducting and exhaust, I should be able to easily plug a new heater in, should this one fail.
Well worth upgrading parts and total cost, including holesaw, £212.
I got ducting, exhaust and some other bits from H Bowers online - good service, range and prices. Mounting plate was £22 off eBay.
It's easy to see where the Chinese heater I got (£102) falls down compared to Webasto/Eber etc, with the electrics not being in a sealed case and some roughness to the casting etc. It doesn't run just as a fan and the fuel pump can be heard through the base of the van. Setting timings, temps etc doesn't look easy, though I'll just fire it up to get up to heat then turn it down to 20deg C. It ticks along quite quietly then. Aside from the fuel pump, the noisiest bit is the air being drawn in through the driver's step. Not sure this will be quieter on the premium models?