Yeah, I hate gloss finishes on kits. Nothing is gloss apart from, as you say new cars and Im sure wartime boats would have been matt, although maybe I will be corrected.
I just wanted to gloss the boat for washes and decals, then I was going to weather it and finally seal it with a matt varnish. I tried a small jar of Humbrol gloss coat and thinned it and applied with my airbrush with no problems. I think maybe a lighter hand with the spray can might give better results.
I have been using Rustall blackwash and it seems very thin. I applied it over the whole boat and then wiped off, and to be honest , more or less the whole lot came off, leaving a not very convincing look.
I am going to try a few coats of this blackwash, plus I have ordered some MIG darkwash. Certainly the MIG brownwash is a lot thicker, but for the hull of the boat , maybe not the best, as it stains everything brown. I am still a bit unsure as to the best way to apply washes, and filters are an even bigger enigma to me. I mean what is the point of filters? Why not just use a different colour in the first place?