Sightseer Bag Question

Planning to use the Vincita Sightseer 4.0 bag to transport my C-Line to Cycle Zydeco by air next month. For those who have used the bag, some questions:

1. Do you use the internal garment bag strap to wrap around the folded bike, or do you just let the garment bag "float" on top of the bike?

2. Is there a way to keep the bike from rolling around inside the bag? Do you pack other equipment in there with it?

Thanks in advance.