I realize this is for your "camp" which I assume is like a summer cottage or perhaps as hunting get away so will not be frequently used. But, your problem lie in the fact this this toilet is what is commonly referred to as a "builder's special". This mean a very cheap fixture that builders buy to install in their spec homes. Many plumbers make a pretty good living replacing these within a few months after the home is sold. There isn't much you can do about it short of replacing it with a better quality toilet. One toilet that would work very well is the Toto Drake. These are not expensive, but are real work horses.