I'm going to go ahead and keep posting updates on my Proton Pack Project for anyone who is interested in following along or is searching for information on how to build one on your own.
At the moment I am doing just basic research on the Proton Pack including how the original was made versus some others that fans of the films have built.
Here are a few of the many links on building a Proton Pack that I would like to share:
A guide from GB Fans on how the original Proton Pack was built and from what parts - a great read!
A Proton Pack replica on Flickr
Instructables: Be a Ghostbuster for Halloween
Electronic Parts for the Proton Pack from Hyperdyne Labs
A cheap and fast way of building one: