The GC is that real reason why it is not very useful to use automatic generated Wrappers. OCC has some strange Management of their Built-In-Classes. They have their classes i.e. V3d_Viewer and the Handles Handle_V3d_Viewer. First I tried to use the pure classes in my wrapper an experienced a lot of Problems. Then I switched to the Handles and everthing worked fine. BUT I had to write two DLLs to get OCC usable in a C# Project.
www.jay-code.de/lo/OpenCascadeWrapper.zip
This is my sample-Code so far. You may feel free to take a look at it.