Roger,
The proxy assembly should have no dependencies other than .Net framework assemblies (2.0) and VSTA assemblies.
As you develop your application and revise the VSTA integration layer, only the proxy assembly needs to be strong-named and installed into the GAC.
Each time the application's object model changes:
1. the proxy layer should to be regenerated and installed in the GAC (to propagate the changes to the addin)
2. the project templates should be removed and regenerated (because the addins must reference the new proxy assembly)
3. the addins rebuilt (because the addins reference the new proxy assembly)
Hope this helps,
Gary