Got a question. What width do I need between the tires on a trailer to haul most any car/truck?

I just broke down a 15 ft camper and kept the deck since it solid. ONly problem is the tires stick up through the floor and I cant figure out how the hell to make something out of wood that can handle the weight of the car going over it. So Im curious if I have enough room between the tires for most cars.