Wilderness Systems Piccolo Repair Advice

I recent picked up a very Piccolo from the 90s. Fits my kid great, but a few small repairs needed.

First is the seat. The seatback is gone, but there are some plastic tabs that had pop rivets sticking up from behind the seat and some strap from edge of the cockpit. The seat bottom has a phone seat glued on. I’m trying to figure out a replacement seat back either from the compatible aftermarket or by jury-rigging something.

Second is is the oil-canning. There are a larger and smaller flattened spot in the hull mid-kayak and just beyond. I heat the large one, pressed out the dent, and weighted with large rock while it cooled. I let it cool over 2 nights, but it went back the old shape the next day when the rock was removed.

I suspect the dent has been there so long it set in the memory? Maybe I need to add some sort of sturdy rib to keep in in the original shape.

Or just leave it.

Appreciate any thoughts on either.