Doug,
Yes you could leave the jams go un- masked, if your using the same
color.  Usually the door seals will keep out most of the overspray, but
I use a liquid mask,  to assure clean jams.
You spray- brush it on, and when your all done painting and rubbng,
etc., you simply take a wet rag, or a low pressure hose, and all the
overspray,and rubbing compound washes off.

Pretty simple, works good.

Or you could just do nothing, and wipe the jams and door gaskets clean
with laquer thinner.

This works OK too, but you have to be careful of not letting the thinner
get close to any of the fresh paint.

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Terry
74 Campmobile (Clementine)
85 GL
86 BMW 325 ES