To make "bunks" cut some Pressure treated 2x8's to 14" long, stack them two high and bolt them onto the trailer crossbars w/ carriage bolts ... cover w/ 1/2"-1" styrene and then w/ nylon carpet. The pressure treated wood is so the wood doesn't rot after 4-5 years ... the styrene and nylon carpet will not retain water and cause gellcoat blisters.

Be careful of placing straps "over" the boat ...as you travel down the highway the straps will vibrate in the wind ... beating against the hulls. That is the main reason I switched to the 4 corner strap/tie-down system. Before installing the 4 corner system to prevent the "hull beating" I wrapped foam around the straps at the appropriate places and then covered them w/ "Knee High Tube Socks that I had cut the toes out of. That worked for several years.

HarryMurphey
H18mag /#9458, Fleet 54/Div11
P19MX w/spin /#86, CRAC