The frequent "low voltage" warnings you are seeing are not from the track voltage being at 13V, they are from frequent small power drops that you may not notice but definitely affect the Railpro module. You can run Railpro on voltage lower than that and you won't get low voltage warnings. I've run mine on less than 11V without a warning.
In my experience Railpro is much more suspectible to power drops than DCC decoders. I'm not sure why that is, but I suspect that Railpro modules draw more power than DCC decoders (due to the RF transponder?). Also, most DCC sound decoders have larger capacitors built in to get over dead spots. Railpro has some internal power storage, but it is very minimal.
Do as Jacob says and install some keep alives right now and never fret about dead spots again. I'm going back and installing them in all my locomotives. When Ring releases his solution I might transition to that, but in the meantime I'm happy with using TCS's keep alives.
-Kevin