If you go through the trouble to remove and clean the carpet area, you could
simply paint /maybe epoxy paint / the area and sprinkle sand to create a
non-skid surface. Not much fun to kneel down on though.

I also once used the "salt sprinkle" method. I painted an area; let the
paint dry...then re-painted the area with a 2nd coat and sprinkled salt on
the surface prior to the second coat of paint drying. When it was dry, I
washed and scrubbed the area to dissolve the salt granules. The pock marked
finish looked very good and provided a cheap, non-skid surface.

I think it is important that you first give the target area a single clean
coat of paint, before the second, salt impregnated coating. That way, there
will still be a finish coat covering, even after the salt crystals dissolve.

I've heard that the spray-on bed liners can be very heavy. I'd also worry
that they might crack, as a boat deck probably moves a lot more than a truck
bed. A bedliner seems hot and heavy for this application.
RG