Identifying Discovery 169 plastics

I am currently designing a unicycle device for portaging my Old Town Discovery 169. I would like to glue a mounting plate to the floor of the canoe but have not had success so far because the glues I tried have not bonded properly. Of course my best bet is to make the mounting plate from the same plastic as the floor and purchase the appropriate glue for that plastic. I believe the brand name for the plastic is Royalex but I would like to determine the actual type i.e. polystyrene, polyproplyene, etc.

It is a specially-formulated polyethylene (I believe high-density linear poly) that Old Town calls X-link, or something like that. It has a spongy core (to add stiffness and flotation) sandwiched inside two solid sheets.

Traditionally, this stuff has been difficult to bond to. Some have used thermal plastic welding.

The relatively new West System G-Flex epoxy has done a much better job (in my experience and per reports) of bonding to poly than traditional epoxies. You should pass the flame of a propane torch over the surfaces to be bonded before use, especially on poly.

Get rid of that tubby, shapeless canoe
and get a light composite boat. Nothing more than 50 pounds. Then get a bicycle.

and not the same at all as Royalex NM

You will have to through bolt it
I tried and tried ways to glue a mast step into the polyethylene Disco 160 I had years ago. No glue or method worked for the strong shearing loads put on the mast step when sailing. It always failed even in light winds. Finally I decided to through bolt the step into the bolt with silicone sealer in the holes and stainless steel bolts and it held up for many years until the whole rig got sold to the boy scouts.