My last van had gas heating and a gas hob, I got it converted from the 907 to underslung and it was great. LPG was cheaper, it could be switched on/off without leaving the van, and I suppose freed up space inside the van. I found it inconvenient to rock up somewhere at dark o'clock, walk outside the van on a sodden parking spot and footer about with the back doors open switching on the 907 in the hosing rain. The other benefit was an internal gauge so the gas remaining was instantly visible.
I had an external BBQ point but it was never used once. At the time there was an LPG pump nearby although this has now gone, although in two years I think I only filled it up once from half full.
My new van has a 907, before the van conversion I asked for the 907 to be placed within the kitchen unit so I can again switch it on/off without leaving the van. I've a diesel heater now and after two years I weighed my 907 to find it still 2/3 full as it rarely gets used - a couple of reheated meals or soup and half a dozen kettle boils a year.
The only drawback I still have with the 907 is keeping an eye on the remaining gas level, I wish there was something reliable that would show the remaining gas inside a 907 without removing it and putting it on the scales.
Summary - underslung was better but the conversion cost isn't worth it for my low usage. I've just priced up an LPG conversion and, at about £900, that's a lot of 907 refills - far more than I'm ever going to buy for this van. At some usage point the LPG conversion cost becomes well worth it and brings greater convenience but I'm nowhere near that point.