My heat ex's work perfectly. Plenty of heat at the windscreen and toasy toes all winter long. The problem is that while I'm lovely and warm in the cab, little r is in the back, too frozen to cry out. Solution: Propex.
My top tip. They occasionally get units returned for whatever fault. They recondition them back to 'new' condition but, do not advertise them for sale. I bought an 'as new' heatsource 1800 directly from them. The unit was refurbed but all the rest of the bits (including thermostat) were new in the pack. All this and a 12 month warranty to my door for just over £200. The gas bottle from my cooker fuels it as well.
Having never attempted anything like this before, I was able to install it myself in about 2 hours.
Put it on the thermostat and bang! Instant central heating in yer bus.
if you're about to lay out the cash for one, ring them up and ask for Roger in Parts. he's yer man.
Edit: A propex is NOT MoTable (as in not looked at by tester). If you have camper insurance (as I do) it is covered, even if you install it yourself. I'd check with your insurer though, as I did.