painting the inside of the mirror box

I have just finished construction of my mirror box of my 16" F5.5 truss scope, actually all of the mechanical parts are done (yeah!). Its now time to start "finishing" it. Any one care to share how to spray paint the inside of the mirror box black, without getting any paint on the beautiful baltic birch exterior? I'm thinking of masking tape (painters grade). But for great results do you attach it to the inside surfaces or the actual edge of the box? I'd really appreciate getting some tribal knowledge on this.

Masking tape and paper is what I use. Mask off the bottom holes too. Make the edge meet the edge of the outside of the plywood, that is easiest. So you would apply the tape to the outside and make it just meet the top edge. Then use newspaper or wrapping paper to protect from over spray and tape it to the original tape line with another piece of tape.
My opinion, let's see how others do it.

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To keep paint from bleeding under the masking tape I put a coat of clear along all the edges to seal it. Never had any bleeding with this method.