use NORON auto body adhesive. make sure you use the ADHEASION PROMOER. apply the adhesion promoter and let that dry for 15 min. then glue in your bolts. then wait till the glue is fully cured. the 5 min glue cures in 45 min.
i use the norton adheasive all of the time reparing polypropeline bumpers without any problems. i have even repared atv fenders with the stuff so it should work on your fuel cell.
i am sure there are other manufactures. 3M fusor duramix and others, who make similier stuff that works great. remember with poly based plastics you must use adheasion promoter or nothing will stick to it.

perception is 90% of reality