is there any way to determine usage of a fifth wheel?

I have found there are also those that buy them and use them full time but don't even own a tow vehicle, so very little road time, or those that tow them all over the country but only a few months a year, and the rest of the time is sits in storage, or even in a garage.

Many variables. I would have to agree that the one that is used, is probably maintained better.

My truck has an odometer that counts miles on each trailer I plug into it, and can even tell which trailer is being plugged in. Kind of cool.