You could also consider Niederrhein-Weeze Airport, which has customs, immigration etc.
I looked into Peter’s suggestion of Paderborn EDLP as it seems v quick and friendly. But I just heard back from then that Jet A there is E2.56! Wow!! Don’t know if that is with or without VAT. I am used to £0.95 per litre in the UK (ie about E1.10). and most of my EU flyng lately has been to Croatia and Italy which are nowhere near those levels.
Is that normal for Germany these days? Is it significantly cheaper in Belgium or France?
Yep, 2.50 is normal for Germany nowadays. Hence the recommendation of ELLX.
Belgium is generally a bit but not hugely cheaper for private ops (the airports often advertise tax-free prices).
France is more like 2.00.
Thanks Boscomantico.