Speaking as a retired gas and oil central heating bloke (NOT engineer, it's only lego and hot air, that's not engineering) my preference would be for a gas boiler simply because by its nature, an oil (diesel) fired boiler will need periodic disassembly to clean out the carbon. A gas boiler won't.
As for refillable LPG, this is one reason I have against having an AutoSleeper which all seem to have underslung LPG tanks which you have to search around the UK to refill. I had one, and the gauge read empty when it was still more than half full, so you start searching, drive 30 miles out of your way only to discover you only needed 5 litres to fill it up. This is another reason not to stay in the UK. Anywhere on the continent when you want LPG you just drive around whatever town you are in searching for the cheapest LPG. You have already saved the £25-£60 a night cost of staying on camp sites in the UK so any holiday over a week will be cheaper than staying here. And the supermarkets have phenomenal selections of fruit and vegetables, quite unlike what we get. And the traffic density in Abroadland is about a tenth of what it is here. And they don't have height barriers (at least I haven't seen any). And you can park overnight.