I would caution you against doing boat seats with all that stitching. If you did it that way, you're just inviting water into the seat cushions and they'll never dry. Also, the sun will play havoc with the thread. There is marine vinyl out there that has 1 1/2" pleats heat sealed into it, but you're going to have a hard time finding the burnt orange color. (You'll have a hard time finding burnt orange one way or the other.) This is called pleated vinyl, or roll n' pleat. This stuff is very expensive, unless you can find a good deal on line.
If you absolutely have to have the stitching, I would just stick to a panel with vertical channels on the bottom sewed to a smooth panel on top. You could separate the two panels with a welt if you wanted to.
No one lives forever, the trick is creating something that will.