I'm working hard on my "Rocket Sled" vehicle.

I finally finished the model (and its collision model). Now I'm trying to see if I can build the physics tag correctly. However, as I just recently learned, the physics tag uses "mass points". I'm interested in learning how to create these accurately. So I take the values for the coordinates and radii of each mass marker and input them into the warthog model to get an idea.

However, the "powered mass point" has no coordinates...how do I deal with this? My vehicle has two skis and two treads.