Larry at Treasure Coast Avionics in Ft. Pierce, FL has a good bit of experience with WX-500s and can tell you a good bit about them. My understanding is that they are a bit finicky about ground planes, which you can apply directly to the glass using Nickel shielding spray. I use the stuff for shielding in various applications.
Allied Electronics has it, http://alliedelec.com
I'm testing a WX500 at the moment, I'll letcha know how it turns out.