Check out one of
Felion1337's builds.(The gallery is in Swedish but the images are very descriptive)
He uses 5 mm foam sheets between plate and PCB, automotive bitumen sheets to fill cavities in the case and electrical tape where things make contact (such as under the Cherry stabilisers).
You don't have to cut out a square for each switch. I have also seen people cut strips that go only in-between the rows.