It'd be nice to use the Skydemon fuel feature in the aircraft profile but I just can't get it to give a sensible number, obviously because the data I'm feeding it is not accurate.

I fly an Xair 582 and work on 15ltrs per hour using - flight time+30 minutes taxi/messing about time per flight+60 minutes contingency. This average calculation serves me well but I can find no way to setup Skydemon to do a similar "Simplified" fuel model in the aircraft profile. 

Any ideas ? TBH I work out my fuel manually, it's not hard but would be nice when planning to have Skydemon do it for me.

Maybe you haven't set up your aircraft's profile correctly for fuel burn? See page 26 of the user manual.
You have to set fuel burn for the following phases of flight:
Taxi, take off, holding, landing and contingency.
I had to experiment with my settings so the SD calculation of total fuel burn was close to what I use, on average, for all phases of a flight.
For me I use around 16.5 litres of fuel for one hour of flight, including taxi, engine run, take off etc. etc.
Also don't forget that SD adds on a percentage for contingency which affects the "litres per hour" fuel figure.

Tony Nowak