I would go the small truck route. A ford ranger would do well for you. If you need any welding or fabricating, I can help you out. I live in Colfax, WI. I am sure we could transform a ford ranger into a mileage machine and even increase the payload/towing by a fair margin. They are decent trucks, but they need a little help
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A stock ranger will squat with 1 person on the tailgate, but will still corner very well. We could get the rear end to hold up it's fair share and still ride nicely. That would help you out in the autocross department. My cousin has a v-6 ranger and they are pretty quick.