The first step was to replace the poly panels with painted concrete panels. This material is often called Hardie Board. Ours were cut from 4x8' sheets and painted with enamel. The panels were caulked and secured with stainless steel self tapping screws. photo 1
Four-inch bolts were fitted into the stud tracks and 3" foam panels were put in place using adhesive to secure them together. photo 2
The foam is a non-absorbent type used in basements. We were very fortunate and got ours from Freecycle. photo 3
PVC shower panels were fitted over the foam and secured using the bolts and stainless steel washers and nuts were used to prevent rust stains. I still need a small piece to complete the entire wall, but most of this material was salvaged from construction sites. photo 4
The result is a attractive waterproof wall serving as a backdrop for our plants that is probably R20+. photo 5
The panels I removed were saved and will be cleaned and added to the other side, doubling the glazing and thermal integrity of that side as well.