I thought I would post a couple videos of my little battery power Bachmann Davenport using my radio control, 5 AA li-ions, and a phoenix P8 with speaker all under the hood.  I'm going to add two solenoids to control the couplers next.  I'll use the hand bars as they work so smoothly it should be pretty easy.  The relays to drive the solenoids will be hung under the loco, there is a limit as to how much can be crammed under the hood.

Quick run to see/hear it operate:
http://www.youtube.com/watch?v=YFIVWewpnZ8

The end shows a view of the inside, like most modern cars, not much room:
http://www.youtube.com/watch?v=zZ-f_ez91Vg

russ