I realize that it may take some work, but can I use my existing Mega, GPS, 3DR radio and load it with ArduRover software and have something that works like an APM2.5 and uses Mission Planner? 

I have an APM 2.5 on my quadcopter and I am pleased with the way it works and integrates with MP.  I have built a rover from scratch (hardware and software), but I am not so pleased with the way it works ;-(

Thanks, any suggestions would be appreciated