Neil
I also think you are over the top with the Gnat. A JP5 burns about 750 litres of F34 per hour (on average). Gnat probably burns about 1000 - 1200 litres an hour. With the price of Jet into your tank at a little over 50p a litre, this will set you back at about £400 quid an hour for the JP5, and £700 quid for the Gnat.
Best person to ask on the Gnat (and the hunter too for that matter) would be the rugged handsome chap from delta jets, or maybe Mitten? You out there somewhere?
