I know what you mean about the doors, so much that I ended up gluing mine closed. Also I should have done some research on the Wagon, I put the glass in mine. Good job on your Wagon.
Seems to be however I try not to handle the model wherever I've used the Sharpie just to be safe. i do believe Snake45 on the forum here is the Sharpie King, if it weren't for him I probably would still be stumbling around with foil. I do have a 64 Thunderbolt that is ready for trim and I think the only way to go with it is foil, grrrr.
Myself and several others here use them for chrome trim with good results. I don't necessary like foiling myself but I do think the results are better with the foil. This is one example of a build with the Sharpie....