I bought a pair of lightweight aluminum dirt bike loading ramps. They are 82 inches long, fold in half and hold 400 pounds each. I didn't want the aluminum ramps directly touching the back of the car so I created a couple of 2x4 wood supports. I ripped 1/3 off the lower support to give it a 45 degree angle from ground. I finished them and put some outdoor carpet on the sides that touch the car and the ground. I put 2 bolts on the top and bottom of each rack and put holes in the 2x4s to hold the bolts in place when the ramps are placed on the boards. I use a elastic cord to hold the ramps up against the car so the upper board won't pull away from my back bumper.
Here's a picture of the ramps and support. If you google dbf-8206 you can find resellers of the ramps online. The ramps have high enough sidewalls to keep the wheelbarrow tires on the ramps. The support boards keep the spacing of the ramps correct for the width of the wheels.