Re: Best way to soundproof engine compartment?
3M makes two "strengths" of foam spray adhesive, the stronger (90?) holds up the heavy 1.5" foam with the barrier in it for about a year and a half on the overhead sections (much longer on the vertical areas). This is in a powerboat that sees a lot of rough water. We bought our sound proofing stuff from Hamilton Marine here in WA, very similar to the stuff that Mitiempo sells in BC.
SV Laurie Anne
1988 Brewer 40 Pilothouse