Adrian - your mention of Sign Painter's 1-Shot is very helpful. I had no idea there was such a thing as high pigment sign writing paint. And in relation to Humbrol, read on.....
I very recently had
one heck of a job trying to get Humbrol matt enamel to cover a matt paint surface - it should have been a piece of cake.
With a top quality fine brush it took 2 coats plus a patching job before it was anywhere like 1/2 decent
It looks awful close-up but from a more normal 'just about to get run over' distance it is passable.
It has been many years since I last used Humbrol enamels and in the past found they gave excellent coverage on a wide range of surfaces - I am now left with the distinct impression they are nowhere near the quality they once were.
I also got a tin of Humbrol matt olive drab for touching up work on the jeep (I took a sample in to match with the tin lid) and found the shade so far off from that on the lid it was unusable (and yes I stirred it well). What is going on in Humbrolworld?
In the absence of a laser cutter I had to print the sign writing on 120gsm card and then cut around it with a Stanley blade. I then used a yellow acrylic paint pen with fine nib to draw around the outline onto the panel - that part worked fine.
I have another two sign writing jobs on similar vehicles soon and will be sure to try this paint - the UK importers are
Signwriting Paints - Paints
Tony