It looks like a lot of fun if you have the room for the track. Warren Mumpower over on large scale central built himself a box cab and flat car to ride on. He has a friend with a track. I'm sure he could help you out.
http://www.largescalecentral.com/LSCForums/viewtopic.php?id=7743
http://www.largescalecentral.com/LSCForums/viewtopic.php?id=7258
makers of the kits he used -
http://www.plumcovestudios.com/
-Brian
The Home of Articulated Ugliness
ive looked at that boxcab before it was nice, but, man the price tag! ill build one my self for that price!
altho the box cab is fairly light i belive there might be a soloution to your problem there.
Get the Garden Railways newsletter delivered to your inbox twice a month