bodykit fitment and mold questions

hey i just got a body kit for a 90 crx and the side skirts are a little short so there is a gap where the rubber dent protector used to be. i dont know if this has happened to anyone else but what should i do? do you think i could fiberglass it to the metal or should i body mold it? im a little skeptical about bondo or other molding becuase i heard it will crack?

will it crack if i fiberglass the kit to the metal ?

also how should i secure the door caps, any suggestions on how to install these becuase i already did front and rear bumpers and they came out great

so if anyone has had this problem or has done their own body work any suggestions or any advice would help