"Our stroller won't fit in those plastic bags that the airport gives out, it's too long, so it's either send it by itself and get it all dirty like our other strollers are, or put it in a bag."
Tecnically, you can use those bags to cover a Mac; you just need two of them. Put one on from the wheel end and tie it tight, then put another on from the handle end and tie that, too.
What I used on my Mac (and my Chicco and my Pliko--I collect strollers) was a ripstop nylon sleeve; just a rectangle of fabric with elastic on the wide ends, and velcro squares down the narrower end. The wheels and handles stick out, but it protects the upholstery and is much cheaper than an official travel case. I can roll the stroller down the jetway with it on, then just set the brake when I leave it by the door. It also has "BABY BUGGY - DELIVER TO GATE" on it in big letters, and it is neon yellow. VERY hard to miss.
Never let a gate agent tell you not to carry your stroller to the end of the jetway; fold it and take it down yourself; putting it next to the exterior jetway door (but NOT blocking the door, of course.) BTW, I don't let any amateurs fold either my Mac or my Pliko; those aluminum frames are way too easy to bend out of whack if you try to cram them shut rather than folding them as they are meant to be folded. Most breakage to strollers comes from airline personnel trying to fold them (or refold them if the clip didn't hold) --play it safe, either bag it or bungee it.