I used the butyl rope trick on my truck and cut the ABS plastic to fit snugly between the inside and outside parts of the hole while sealing with the butyl rope. Another product available called Nutsert Threaded Inserts (rivet nuts) can be used to make the ABS, PVC, or whatever you chose to cover the hole removable like an access panel. https://www.edfast-online.com/Thread...ts-s/24991.htm