I had a somewhat similar problem with a Navpod that was originally fitted to my sailboat. While it was made by Navpod, it is a discontinued model, which meant that finding a replacement top cover for my badly cracked one with a wrong sized hole left by the PO was not possible. Instead of replacing, I took the top cover off, added extra fiberglass
on the back and everywhere the cracks were present. Patched the holes from all instruments. Did 3 coats of new gelcoat
on top, sanded, buffed and then cut new holes. Looks brand new right now. yea, it cost me about $50 in materials and 4-5 hours across two-three days, but it was worth it.