looking for best 5th wheel for 1/2 ton pickup

I've been looking at small 5th wheels and my preference is a late 80's - early 90's 17-20 ft. I haven't found one locally (with in 200 miles) to buy so I started looking at 22 ft models because they are fairly common. Try as I can I cannot see any way the numbers work for a 1/2 ton. 22 footer's average about 4000 lb dry so I figure they will be 5000 lb when loaded. 1000 lb pin weight doesn't leave enough cargo capacity for people, dogs, fuel, etc. on a 1/2 ton. If you can find a used 17-20 ft the dry weight should be about 3000 lbs and the numbers work. Since the manufactures of trucks over rate their MPG to sell trucks I assume they do the same with cargo capacity. Meanwhile trailer manufacturers under rate their wight to sell trailers so I like some cushion in the numbers.