Here's why rustproofing really works...

The trailer is 15 years old and has been stored outside for that entire period.

It has not been used for over six years. The safety chains and the links have not been unscrewed for all those years, but the screw on nuts have been sprayed with rustproofing 15 years, ago.

Today, I went out and tried to loosen the screw nuts. They moved better and smoother than when they were new.

So, as rustproofing works, I always spray assembled bolts with penetrating oil and bolts with rustproofing before assembling them.