RV /Trailer backing plate for shower valve

Decided to install a thermostatic mixing valve in our RV.  The mounting surface is thin fiberglass so created this backing plate to add reinforcement. It is designed for fixtures with a 4" center to center spacing (100mm) between hot and cold, ½" MPT.

I've included the Openscad source to modify as needed.

It was printed on a Prusa MK4, Prusa PETG (Signal White), 0.20mm QUALITY, 100% infill, No supports, no brim, textured surface cleaned with Windex.