we just got our travel info from make a wish, and we're flying southwest. southwest.com says all strollers and car seats that are going to be checked need to be in a bag. Can I just use like a heavy duty garbage bag? I don't really want to spend $45 for 3 gate check bags. What are your tips? we were planning on using the strollers through the airport to make life easier, so we need something simple so when we get to the gate we're not fighting with a stroller bag. we're going to have a mid size stroller (evenflo journey), and umbrella stroller(maclaren) and a high back booster seat. tia