Fiberglass resin and abs plastics work very well together, just use a mat fiber backing and it will literally be stronger in the repaired location than in original condition.
I also like to use the mat fiberglass as apposed a roll because for some reason it just lays out flatter and wont curl on you. sand and paint with any combination of rattle can paint or rubberized bed liner is awesome, just test it on something else first for how much stippling it has after its dry. different brands, different end result.