We tried renting a few times. It may not make sense but it bugged me beyond description to have to fork over the extra hundred or so, for a car rental, in the middle of a trip. It seemed that there was always something that would be better to spend the money on (beer, food, amusement parks).
It cost me about the equivilent of 15 rental weekends to pay for a dolly and equipment but personally I was happier with the one time expenditure as opposed to the car rental which seemed like death by a thousand knives.
Now if a boat was important to me I would likely put up with the rental costs and enjoy myself on the water.