Just wondering if any one has ever added cocoa powder to a boxed pound cake mix. I'm considering using the 3D Wilton Train pan but didn't think my usual chocolate buttermilk cake would be substantial enough to keep the train upright. Also, didn't really want to make a whole recipe of chocolate pound cake from scratch because of time and too much batter. Any suggestions would be appreciated.

I have but more to boost the chocolate flavour. If I want a really dense chocolate cake I'll use this one:

http://cakecentral.com/recipes/15158/triple-chocolate-fudge-cake
And if you're carving, you could leave out the chocolate chips if you're worried they'll make it more difficult to carve.