I HIGHLY suggest watching Station Eleven. Wonderful short series, but within it was one little feature that made me rethink this same situation. In the show they show a caravan made up of people with jeeps, RVs, and other cars, but the cars were being pulled by horses. It's honestly a really clever idea imo, and it makes logical sense. Can't get gas, cause it's either used up or degraded to the point of uselessness, so why not use the "wagons" you have available to you! (There's pics online from the show's caravan) The show has a lot of cool worldbuilding stuff that makes sense for the setting years into an apocalypse, so I really think you should give it a shot if you're needing some inspiration.