Styrene is a very tempermental material. It doesn't like harsh solvents,which the base of the truck liner is solvent based,even moreso while in spraycans so it will propel. You might be better off to get some mineral spirits and clean it off completely to avoid further complications and then patch the crack from the inside with a strip of spare styrene.
I'll keep my fingers crossed for you,but in an instance I had of similar nature I had resorted to placing the items in the freezer for a couple of hours and then out in the sun....the extreme temperatures shocked the material into finally hardening up. I tried waiting it out for days at room temperature,but after I started the freezer/sun method all was well.
Good luck
Steve