[Big Dave]

Phil Knox (aerohead) played with using part of a real boat to make an aerolid. He may have other thoughts but IIRC it worked pretty well.

How long is your bed? If it is 80" long you'd probably need only 8 foot or 8 foot 6 inch raw strips.

I don't see why fir strips wouldn't work. Steaming the strips would help ease them into shape and reduce any tendency of the lid flying apart in the future.

A crude lid is not too tough. I made one single-handed in two days using plywood and rubber stair runner material.

But long-term, crude doesn't get it. I couldn't see out of mine and was restricted in my access to the bed. I needed a lid and sort sort of window.

If you can get help from the old canoe-builder making an aerolid with a working lids is certainly doable.