We are getting the pool fixed ($10k cost its 70s fiberglass pool).

Then you do fiberglass mesh tape on the joints, including those back-blocked butt joints.

This stuff is a fiberglass mesh of some sort that is impregnated with tar, so it definitely is troublesome when used for waste lines (might not be so bad if for a stormwater system).

it is fiberglass... oh and we used Durock concrete board as the backboard. 

I'm doing a fiberglass roof deck on top with a 36" high parapet around the whole thing.

It should be pretty simple to have some galvanized sheet metal attached to a standard cover. 2 piece so it hinges. 18g or maybe 20g should do the trick without being too heavy.You could also look at these - https://www.tuffspas.com/tuff-top-cover/ Supposed to be tough fiberglass covers.

Hey GangCheck out some of the excellent demonstration videos both animation and live footage on ;"Trenchless Pipe Replacement" and/or"Pipe Bursting"Very informative,,,I do these type of jobs in So Calif so I can speak with some authority on the subject,,,Again my purpose is to strictly give good information and adviceI like Trenchless as opposed to "pipe lining" because with Trenchless youre actually getting seamless New Pipe and Johns Manville guarantees the stuff 99 years.You can drive a Mack truck over it and it returns to shape.With Lining all youre doing is creating a fiberglass liner inside the original "ancient" clay pipe cracks and all .Hope this helpsDD in L.A.

Be careful if you drain the pool, it looks to be fiberglass.

What you see in the wall is actually the back of a fiberglass tub.

If you can't get a single fiberglass unit in the opening I would recommend getting a shower base and tiling the walls.