Yes, might be OK, but ... "Municipal plant" + "Stainless Steel" likely means something corrosive going on there. "Improved" NEMA 3R might be fine, might not. Without knowing, I would not want to second guess that issue and create problems down the road.
Weep Hole Tangent: I once did a large project where I built 142 small pump panels in sealed outdoor boxes (so they were gasketed doors) and drilled weep holes in the bottom. But I wasn't the installer and the guy who got that contract tried to save money because of the mistakes he made that got him the job. So instead of making a concrete anchored strut rack to mount each panel, then run 3/4" conduit in and out as specified, he used a single piece of 3" conduit as both the chase for the conductors AND the mounting support by using a sweep ell through a poured concrete block. Problem #1 was he used my convenient little weep hole as his pilot hole for the 3" Meyers hub. Problem #2 was that he had me remove the alarm beacons from on top of my panels because he was going to find cheaper ones and mount them himself. Turns out they were cheaper because they were INDOOR, not outdoor. Problem #3 was that he had to put in a Chico seal on the 3" conduit because the output wires went to a wet well. So the fixtures leaked, but because the weep holes were gone and the conduit went through a sealed Meyers hub to a Chico seal, the water that leaked into the beacons had no exit and completely filled the conduit, then the enclosures. I got to sell the panels twice...