Transom help On a v20 center console

[drj]

The Guy i bought it from said he had cut the transom and that is why it rotted. he cut it because he "got a good deal on the motor" which ended up ruining the transom. Somebody told me about a structural composite board that i can use for the transom has anyone heard of it or know where to get it. I am still considering seacast. i am still continuing with the project while i decide on the transom. I have been sanding and grinding and filling.