Update:
Folding and securing the EPDM liner
Putting on the composite decking boards over the liner.
Assembling the tank lid. It's in 2 2ft by 4ft sections. I didn't have enough extra EPDM, so I used 4 mil plastic folded over itself in multiple layers and stapled down. It shouldn't reach the plastic's melting temp, and will see how it holds up over the years.
Lids in place, the nearest decking board isn't attached yet at pipping for the 2 pex Heat exchangers and 2 pump lines are yet to be put in.
I also ordered 2 300ft rolls of pex from pexuniverse and they're on the way. The next step will be integrating the storage tank into the existing plumbing