I have some projects that require full sheets of plywood once in a while. Unfortunately I don't have a good way to get it back to TechShop so I altered my luggage rack so that it can safely accommodate a 4x8 sheet of plywood.
I did this on a Ford Escape but the process should be similar for other makes and models as long as you have a luggage rack.
I made it at TechShop.
Step 1: Gather Materials
For this project, I used some 2x4s that I had leftover from another project. They measure 7ft long which happens to be perfect for my car.
You will also need some ratcheting tie down straps. I picked up 4 at Harbor Freight for $14.
Step 2: Cut the Wood to Fit Your Luggage Rack
Put the wood on the rack and outline where your notches must be in order to fit snugly and lock into place.
Using the bandsaw, make some relief cuts to your pencil line. Then, cut along the line to complete the notch.
Step 3: Add Your Plywood Sheet
Now, you have a flat surface for your new lumber to rest on. Put the plywood on top.
Secure the plywood by tieing it down to the luggage rack underneath. Ratchet it tight to prevent any movement while driving. Be sure to strap it down in such a way where the wind won't be able to lift it up. For this, I've run 2 straps from my front bumper to hold down the front of the plywood.
Drive carefully. No highways! Avoid long distances. Fortunately Home Depot and Lowe's are just a mile away from TechShop Detroit for me.