How to add cockpits to XSP ships that don't have them

[captainradish]

I've been scouring the web trying to find an answer to this and haven't come up with much. I use XRM with the cockpit mod which adds visible cockpits. I have found a bunch of XSP ships that are utterly lacking cockpits (they were never made with them). I already know I can modify these ships using the package creator included with the plugin manager (and have made many ship tweaks successfully). However, adding a cockpit is eluding me. When I copy and paste a cockpit from another ship that has one, the package creator crashes when I try to modify it further. What am I doing wrong here? I have some truly wonderful ships that I cannot use because they are missing a simple line of code in the XSP file.