I've had good luck with Moeller tanks, huge selection of poly tanks on their web site if thats what you're looking for.

Great Lakes Skipper and Jamestown Distributors sometimes has them on sale.

I looked in the vendor forum hoping to find a fuel tank supplier and did not. Is there more than one vendor? Surely I am doing this wrong?

New member looking to seek inspiration on boat builds and knowledge about fiberglass work as I’m interested in possibly doing a restoration on a 222 one day!

Yeah, livewells sink a lot of boats for sure. Will cross that bridge later.

2023-A-194-00047  Drainage Permit Number 2023-D-194-00050

The coosa on the stringers will work but the factory trapezoidal stringer shape is pretty strong once they're filled with foam.
I added a strip of glass, probably 1708 that was 4 inches wide, along the inside of the stringers where they met the hull. There is no 'liner' inside the stringers so you're bonding straight to the hull. That actually made a noticeable difference in the wall stiffness.  Wet the strip of glass on a work table, roll it up then bring it up into the boat, nice and easy to get it into the stringer through those little access holes then unroll along the seam. Just be sure to place it mat side down.

The factory foam within the stringers seemed pretty light duty, maybe a density of 2lb/cub foot type foam?  I used a denser 4lb/cf foam its much much stronger and more waterproof. Added weight is minimal probably about 20 pounds more for both stringers than if I used the lighter foam. That might be a better way to go vs. bonding coosa to the stringers.

For the livewell, older Mako's did the same thing, with a plumbing system that let you draw in seawater from outside OR shut that down and recirculate the water within the livewell. Even if overflowing into the splashwell you'll still need a way to get all the water out, drain plug on the bottom of the livewell that drains into the bilge? It's a great idea when it works right. Or it can sink your boat if the plumbing fails.