I never place any projects in the 'ca\' namespace, this is the place only for BI's original material.
Your project folder should be in p:\ along with the ca folder, they should both be in p:\ root.
You can then reference in your project those models and textures you need from ca without a problem provided you have set everything correctly.
In order to get ladders and other objects working, the classname in the config for the model must begin 'Land_', the rest of the classname being the modelname.
For example you have a model that is called superhotel.p3d, which maybe has ladders and other effects like opening doors, then the classname in the config would be 'Land_superhotel'.
The reason the models in the ca folder already do this is because they invariably have the 'Land_' prefix already applied for you in their configs.
In my projects in Visitor, I have Folder - Textures set as P:\myProjectfolder\data
In my projects in Visitor, I have Folder - Objects set as P:\
So whatever project I am working on will reference objects from any folder in P:\ and will use textures I put in the projects data folder.