I wonder if the quality of current (possibly China made) v belts has gone down like everything else since the 70's. The reason I say that is that I don't remember having to tighten belts all that often back then, or now. In fact, I learned that I was actually over tightening them at first and they actually do better with 'a little' play normally an inch or so up & down in the middle between pulleys. If yours were loosening up more than that I agree you probably have loose fitting bolts, etc. If yours squeal before being fairly loose, you might have a bearing going bad, too much friction somewhere.
Later, Jim