lanchester trailer sells them. by single wheel you mean 4 tires right? the lightest deckovers are aluminum. I priced them before. $7400 for a 20 foot with 4 foot beavertail. they weigh about 1800-2000 lbs. a standard steel will weigh between 2800-3200 lbs depending on length and material thickness.
expect to pay $3800+ for a new steel deckover. get at least a 20 ft deck + beavertail. I have an 18 ft that is too short. I need to load the truck, get out and flip the ramps up, and then get back into the truck and back it against the ramps to set the weight right. 2 more feet would be awesome.