I second the suggestion to consider building a cart that comes apart. My favorite is the team with the two tool chests and a top table that all snap into place and can be easily broken down. During the off season, you may be hauling your robot to demostrations and you want to be able to easily transport in a variety of vehicles.
Also there is a team
that built a new cart last year, not following a lot of the advice given above. It fit fine in the baggage hold of the bus, arriving to their first competition. But then a different bus came to pick them up and it had a smaller baggage hold and the cart did not fit
, which created a long stretch of time involving backed up traffic and many debates. A real learning experience.