Shorty, TJ, Bruce and myself all reside in Nebraska and have had great success with RES. Shorty and TJ are certainly the guys to talk to about it as they really know their RES. I put mine in 3-4 years ago, and by the beginning of year 3 nearly 50% of the ones I caught were over 10". I'm almost certain since you have a sandpit that there is some warmer water toward the bottom in the winter time where they can seek refuge and not only survive, but thrive. Shorty did have issues with some winter kill in 2016 if I recall correctly. So hopefully he will chime in here and discuss that.
One word of advice I would follow or at least attempt to, try to source your RES from someone in Nebraska. It may increase your chance of survival with the assumption that fish with northern genetics have better genetic makeup to survive the harsh winters.
