We've had similar issues of settling bins.
So the last six 5000 bu hopper bins we put a 16" clay base, then laid down woven geotextile, then put 8" of 2 1/2" crush gravel. It's been two years now and skids have only sunk in about an inch. The geotextile prevents the rock from pounding into the clay and disappearing.
As we have a very flat spongy yard also, I'm planning to do the complete yard this way. I can't remember off hand the cost, but considering that we've spent thousands and thousands of dollars over the years for gravel it seemed very cheap to try it.
If you're interested we got the rolls from Keymay Industries in Sherwood Park, Ab Ph:1-780-417-1980
Cascade Geotechnical and Nilex, both in Edmonton also handle it.