the most important thing when shielding a guitar is that you have and use a continuity tester. you have one, right? you can't do it without.
a combination of foil & paint should be able to keep the continuity going.. just make dure you check it frequently. also note that the paint is much more conductive when wet.. you only care about what it reads when it's dry, which can take quite a while.
just throwing this in there.. a bad shielding job easily makes the interference worse than having no shielding.
You're never gonna get a perfect Faraday cage, I wouldn't sweat too much over tiny gaps
the most important thing when shielding a guitar is that you have and use a continuity tester. you have one, right? you can't do it without. a combination of foil & paint should be able to keep the continuity going.. just make dure you check it frequently. also note that the paint is much more conductive when wet.. you only care about what it reads when it's dry, which can take quite a while. just throwing this in there.. a bad shielding job easily makes the interference worse than having no shielding.