Daniel, the tech is correct that some surge protectors/ems do give a reverse polarity warning when it's not always the case. We have other threads on this, and I will try to find them.
However I wouldn't want to just discount it and totally take his word for it without further checking.
120 volt Reverse polarity in itself usually will not give you a problem as far as your RV is concerned for operating purposes, unless you also have a ground issue, then it can be real bad.
Here are some good links to peruse. I use the myrv.us link below a lot and made a analog outlet tester as it shows how to under the outlet testing tab. Having an outlet tester like this would also confirm or deny what your surge guard is showing. This is a great site to bookmark and learn many electrical aspects from concerning your RV. You can also use a multimeter to check for reverse polarity at the outlet, and is explained in the link below.
how to make a 30 amp analog outlet tester shown in the link above;
Mike Sokol (whose is a member here) also has a great website and even a handy book you can get off Amazon that makes it easy for the novice Rv'er to understand and test for electric anomalies, some of which can be fatal. This link is to his website and you can peruse all the sections he has there.
RV Electrical Safety now available in Paperback and Kindle formats | No~Shock~Zone
Mike also touches on reverse polarity in this thread, which we keep as a sticky in the electrical section, as it also concerns hot-chassis condition.
So in conclusion, your surge guard could be telling you that you have a problem where you don't....or it could be correct. What brand/model is it?