Duragrouch

I wouldn't use just a cheap plastic garbage bag, but one touted as high strength, or something thicker.

I was pondering something similar the other day: Arrive at the airport with my folding bike, wheel to one of those kiosks that wrap your expensive luggage in industrial saran wrap (used on palleted goods), quick wrap in moving blanket (cheap, can discard at each end and buy another), then have them wrap it, they usually do in both directions for full coverage. I don't know the fee for that, but probably not too much. Oh and have a luggage tag on the bike in case it comes open, and airline luggage sticky tag will be on outside.