Don't store a dyed backdrop in a bag, dyes are organic compounds, and you could end up with a smelly backdrop. There are better ways to make an impression on your clients! Let it breathe when in storage, dry shelf in the studio or basement will make it happy. For transportation (especially for oversize backdrops) get a gym or hockey bag or use a construction-grade garbage bag (Home Depot has them).
Don't fold backdrops (you'll see the creases in photos), instead crush pack for transportation. Creases will be random and less likely to show as distracting lines in photos.
For very smooth look backdrop (canvas-like portrait application), iron the back drop on cotton setting, then duct-tape one end to a plastic ABS pipe (Home Depot, gray or black 2" pipe) and roll up for storage and transportation.