1- Get a plastic barrel that can be cut up. Take a skill-saw or other cutting tool to cut the barrel in half.
2- Get 2 U shaped bolts to bolt it onto the dolly. Simple.
Step 1: Now Just Use in Areas Required.
I don't own a wheelbarrow, so this conversion has helped me so much doing work in the garden.
Step 2: New Planters
Do the same again. Take the other half barrel and cut in half again and screw it onto a back board. Then fill with compost and plant lovely flowers etc once the spring comes.
So one barrel has made a wheelbarrow and 2 planters. All for free.