Is there any long-term fix for this? Or do I just have to wait for improved LTE coverage (or keep LTE turned off in those areas)?
It's just the cold hard facts of where the state of cellular radio technology is today. It's pretty amazing as is that the iPhone 5 can be so much thinner, lighter, support a larger hi-res screen, be twice as fast, and support LTE. The spotty LTE issue is just one of those compromises that I don't think much can be done about.