When using vinyl tarp for binding edges, use an adjoining technique rather than overlapping the two binding segments at the corners. This is because if you are overlapping the two bindings, you will have four layers of binding alone to sew through. It will be five to six layers in total with the material you are binding, and your machine will likely balk at sewing that many layers. My sewing machine stops feeding the vinyl and sews a big old knot!
Design-wise, use square corners instead of rounded corners when using vinyl binding. Vinyl binding is not flexible and won't bend around a curve like twill tape will.