taking my top off...one or two straps?

As a kid I had a train setup on a 4x8 sheet of plywood suspended ironically above my dads 67 Dart. We used one rope for each corner. The 4 ropes come to 4 pullus that followed down a post in the garage. Never had an issue having the thing go up and down flat. I have a bicycle lift (harbor freight special) it uses one rope and sometimes the front goes up first and sometimes the rear.

I would go for the multiple rope setup!