A long time ago I did this Porter upgrade and used a little plastic coal car as the tender to haul the TMCC board.
For better track connections, I added a roller and chopped out a chunk of brass sheet to make axle wipers. This worked very well and didn't add a lot of friction to the wheel rotation, important for a small and fairly light tender. Wiping on the wheel sides adds a ton more friction, which may be a factor.
