[Ryank]

Having just recently spent alot of time at trailer shops and purchasing a used 23 aluminum trailer I hope I can help.
First if you plan on a float on you dont need rollers. Out of 20 rental trailers at a friends store ranging from 18 to 40 ft not a single float on used rollers. all of his bunks were 8- 10 feet long 4 inches thick and 10 inches high. The centerline on all of his were directly on top of the Trailer beams . The height of the bunks helps to keep the boat from making any close contact with the trailer. and up near the bow before its rise there are either another set of smaller bunks closer together or a cross bunk with a "V" notched out and carpet or that slippery plastic screwed into the "V" Hope this helps
RyanK