Check out Northern Tools. They sell an awful lot of part for do it yourself
I don't know how heavy a vehicle you are going to haul, but don't overlook
trailer brakes. When you do some serious comparison, it may be cheaper to
buy new purpose built for trailer stuff than trying to convert truck stuff.
Northern has some good axles, hubs, backing plates, electric brakes and
controllers. I built a trailer with electric brakes that I used to tow a car
and race stuff behind a Nissan Maxima. My guess is it was close to 2500 gwt.
(more than Mr. Nissan would like) but with the brakes properly adjusted, it
towed and stopped like a champ!