Our old '73 C10 used to haul a lot of steel, but it sagged quite a bit. I don't know what the actual capacity of the axle / wheels are on the truck, but like the others have said the biggest 5th's are going to have the problems, not the smaller ones. It would be terrible if something on your truck broke which damaged the 5th you were carrying. I don't know how large your CG is, but perhaps you could design a few sites to handle the large rigs, leaving the more difficult to maneuver to the smaller units?
I have a 35' 5th and while not the largest, I stayed at a CG which had sites large enough to handle 45' trailers. They put me in a spot which I barely fit into. I am very experienced with backing and it took 20 minutes for me to get in there. To get out, I had to ask the neighboring campers to move their cars the night before. Needless to say, I will not be going back there again, just something to consider.