I'm sure it will come out great, poly tanks
are nice, but I might have just re-habbed:
* Cut the lid out and glass in a flange for reinstalation. A few hours spread over several days.
* Add baffels if needed (prelam FRP). Smooth fillets. No such possibility in the poly tank. A part of the prior project.
* Clean, sand, and re-line with rated lining. A few hours spread over several days.
* Add deck
fill and overflow/vent (remember to put a screen
in the vent to keep bugs out). Make certain the ocean cannot come in. An hour or so, if you remembered to start this when you pulled the cover.
I've built FRP tanks
and been happy with them, so....