There are any number of plastic welding tools out there. They work similar in principle to TIG welding, only using hot air instead of electrical arc. You heat the area, use filler rod, and work your way through the crack.
For finish you could use a vinyl repair kit with the grain texture tools to smooth and matchthe area. I'd think bedliner would be too rough and irregular for an interior piece, unless the rest of the interior was done in a similar finish.