I actually used MDF 3/4" board, I was told it would resiste water really well, much better than particle board. Also I sealed it up with Elmers, water proof wood glue and allot of pre drilled wood screws. Maybe not the best, but works fine. I don't expect them to last more than a few summers pluse since their under the seats they shouldnt get wet very often, but I only have $35 in the two of them.
Cathy, I will be on the water by around 1pm friday, my cell # is 540-915-0432 Jims is 919-434-6561 See you soon