Starts, stalls then wont restart. '89 with LPG kit

[syncro up]

Hi, I'm looking for some advice.
We took the new van out for its first camping trip this weekend and everything was going well until the next morning when we went to leave.

I went to warm the engine up before we left, she started fine and ran no problem for 20 seconds until she stalled... and then refused point blank to start again. In fact it was about 2 hours later that she finally started and was fine after that. Whilst trying to start her, she sounded ok, the engine was turning over and the battery felt strong, but she just wasn't catching.
Well she did the same thing 2 more times on the way home, she would start, I'd leave her to warm up, then she'd stall, then take some serious persuasion to start again. She also stalled once on the way home after driving for an hour, least that time she started straight away.
I've only had the van a few weeks but so far we've only had this trouble where she's left to idle to warm up, I don't seem to have the problem is she's started then driven away.

Shes a '89 2.1 petrol with LPG kit
Usually she was on LPG when she stalled, I could understand if she was cold and stalled, but why would she be soo...soo difficult to restart? Could it be some dirt in the fuel lines?

I don't know if this is related, but we also tried the petrol night heater for the first time on Saturday night, now that started ok then stopped after 20 seconds, even although the timer showed it as counting down from 60 minutes. It has been suggested that there might not have been enough power in the leisure battery, although I'm not so sure.

Any advice would be great full,
Cheers
Alastair

[steve8090]

Not sure of which van this is, if you've only had it a couple of weeks, do you know who did the conversion, more than happy to help whether its one of ours or not, please feel free to call me at the workshop on 01244 389344 and I'll try and talk you through a few things.