ian, i tried a green house heater a few years ago, nothing but smoke lining the roof of van, unreliable and couldnt seem to get the heat right , often i would check and the flame had gone out.
i bought a propane heater yesterday £96 00 with bottle of gas , but on low last night van nice and warm this morning , a touch of condensation thats about it , s imho providing its placed correctly and not directly face ing any thing to combustable it will be fine .
geoff