Air Brake Calipers....YIKES !!! (UPDATE)

On the other hand, you might be looking at something that is an extreme rarity and suggesting that it's a typical expense. Just for giggles I called a shop that specializes in MH repairs and asked how often they had to replace a DP caliper. I was told they did perhaps three in the last ten years and all were caused by misadventure.

To me, that's not something to be concerned about and certainly not justifying buying a spare.