this is old thread, but seen you talk about GUI and wanted to post a link here to my more current MayaPandaUI I redid a while back so it actually works, lol. [url]Updated MayaPandaUI Interface - Egg & Bam Exporter for Maya]
This one should work on numerous Maya builds as I’ve used it on 2012x32 up to current 2015x64. Might be a nice thing to have this working version included in the Panda3D releases for others to have easy access to?? 
~Sean~