Rejex is best applied directly to clean surfaces - no sense in putting Rejex over wax. Rejex lasts longer than wax, so you lose the Rejex as the wax goes.
http://www.corrosionx.com/rejex.html
PlastX on your plexi glass :
http://www.meguiarsdirect.com/product_detail.do?q=4596, then RejeX over the plexi
And WaveAway for your GPS:
http://waveaway.com/