Cut the width of the plywood to fit inside the wheel wells and cut the length of the plywood to fit the length of the truck bed.
Measure the distance between the bolt holes in the fork mount and drill two holes through the plywood to attach the fork mounts with bolts and nyloc nuts.
Fasten the fork mounts to the plywood and load up your bikes! Click through the next steps to see additional customization ideas.
Extras: You can drill a matrix of holes in the plywood that will allow you to attach the fork mount in numerous locations. This will allow you to customize the positioning of each bike.
Cutting the plywood short in width & length allows the bike rack to slide to the tailgate for loading bikes and forward once bikes are loaded. You can also move the rack to make room for other items.
Add a third fork mount to carry three bikes! Mount the third fork mount in the middle at the opposite end of the rack to leave adequate clearance for each bike's handlebars.