question involving transom core

[highstrung]

I have a 20 seacraft 86. I recently purchased a new engine (newer) . Before i go ahead and put the engine on i decided to have my transom rebuilt. i found a guy that is going to do the job for me. from reading through pages of transom rebuilds on this site i am comfortable with the approach he is taking on the re build. only thing im hesitant of is that he said he was going to use one inch thick expandable pvc board as the coring. Has anybody ever heard of this being used for a transom? Also he mentioned placing three seperate pieces in compared to one solid piece. Then glassing them together after being fibergalssed to the inner skin.