Sure, use it! You'll likely have to screw and/or lash the stringers to the frames, unless you have some sort of mysterious umhwp glue. I often screw my stringers to the frames, and it's not an issue.
The plastic frames will be heavier than the plywood ones - but there's no real reason you can't use it. Should be pretty stout, if heavy.

Of course, there ARE other ways to make a SOF kayak that don't involve plywood or plastic at all . . . .

Good luck!
Dave