I would go with a NH dolly wheel rake. They can be pulled with horses easily. If you have a for-cart then just hook up and go. If not then just remove the short tongue and make a longer one to use with your harness. I have also seen a seat put on the front of the rake with just a small angle bracket.
I have pictured one here so you know what I am talking about. The 56 and 256 both can have a dolly wheel setup.