I think I've got it working... I think the problem was with both the .cpp and .h files using '#include "RunningAverage.h"' instead of '#include <RunningAverage.h>'. With those changed and the (:language=c:) removed the program compiles.
I need to pick up my kids and make dinner now but I'll upload the code to the arduino with sensors in a couple of hours and test it for real. Im hoping that I can do this for 16 channels without running out of ram on the mega...I'll find out tonight.
Thank you so much for helping me through this. I think it's time I picked a little knowledge in C++.