i always spray mine, takes a bit of time and patience but always come out nicely

get some tamiya 6mm model masking tape, a sharp craft knife and some a4 printer paper.
dont ever use the actual edge of the tape, i stick it over the gap then run my fingernail down the gap to press it in then use the knife and go around it, press it in with your nail again and repeat till its all done.

the tamiya tapes 3 or 4 quid a roll so thats why i use the printer paper to cut into shapes to cover large areas, once its all done just make sure theres no bits where the paint could get through to the bodywork and give it a few light coats of flat/matt black

heres a few ive done this way





dont get me wrong a brush will work but it takes just as long and a good few attempts to look right, this is better i think