Looking to replace the old benches on my 1964 Crestliner Commador Speedster. It had plywood benches that were wrapped in vinyl. The dash was made the same way and I removed the vinyl off the dash and stained and sealed it. Looks good so I am wanting to do that to the benches but they are in bad shape. What would be a good wood to use? I have available to me plywood, oak 12 inch boards and redwood 12 inch boards. I am just not sure of using solid planks for fear of them splitting on me down the road and don't want to do it in pieces. So what would be a good grade of plywood to use if I seal and finish them with a spar varnish? Would marine be the way to go or would a exterior plywood be fine as long as its sealed well? Thanks, Jim