I use the blue strap pictured, but instead of running it up over the top tube/seat tube area I run it through the wheel and wrap it once around the tire then I pull it snugly. This is not a ratcheting strap, it works great and the bike doesn't move.
The bike is too long, also, the head tube angle puts a considerable lean on the bike. I did a test ride with the gate up and the rear will on the tailgate and strapped down, no problems but it isn't the recommended way and will at a minimum, eventually scratch the plastic cap.
Up to three should fit. I have two, haven't installed the second one yet. BTW, I tested it with the tailgate up, it would work with a strap but I didn't want to damage the trim.