[Garret]

I think you may want to increase the vertical dimension of the frame members (1x2 instead of 1x1) and then add bearings for the wheel axles, the way it is now with the live axle going straight through the frame member will not work (at least not work well). Also you should probably get the live axle hub into those wheels instead of the bearings for a dead axle.

Another thing you should probably do is add a gusset on top of the outer frame members in addition to the ones on the bottom. Doing this should really increase the strength of the chassis.

As always you should consider whether or not you need that much material for whatever application you are using it for, my guess is that you could drop the thickness in a few areas, though its hard to tell from the picture.

It's a good start nevertheless.