See the link I created below for you. We just built three of these. They are easy and sturdy. You could reduce the width a bit to save space if the racks were 'side by side' but I suggest you do not. You can fit a dolly underneath at the current width.
We built racks for our Sunfish at MYC that hold them vertically. It was a great idea to save space, however it takes 3 people to put a boat in the racks. Do something that is horizontal, it is much easier to handle the boats.