When I was buying my boat I schemed all sorts of ways to tow it - uhaul, rent-a-truck, enterprise, etc.... I realized in the end that ALL were BAD BAD BAD ideas from a stability and liability standpoint - and I was only hauling a 35.
I was able to find a place that rented dually's for the purpose of towing. The price was affordable - only reason I didn't do it was because I realized that I needed a truck afterwards anyways.
In summary - either pay someone to move it, or get the right equipment.