Was it petrol fumes or exhaust fumes?
Exhaust fumes means you need new heat exchangers (generally speaking)
My van heating smells of petrol for about 30 seconds after starting, then it clears up. I'm gonna get a carbon monoxide alarm (like a smoke alarm) to keep in the van on monday. It shouldn't (and mine doesn't) smell of exhaust fumes so I suspect fuel or oil is dripping into / onto my heat exchangers or into the heating system somehow. I'll check it out over Christmas on my van.
I do find my van heating, now it is connected up, is just about enough to keep the temperature sensible. I wouldn't call it warm but I was on my own and the rear vents were open. With them shut, all the hot air going to the front I would hope it would be even better.
Stock heating takes about 10 mins to warm up I have found. So it is useless on short journeys, but excellent on motorway cruising.
I tend to stick to about 50mph too, obviously driving faster would increase the airflow through the heat exchangers and keep the van a bit warmer.
From reading other peoples posts, it appears the reproduction heat exchangers are no match for genuine german heat exchangers in terms of heat output.