I will throw in a Saris riser block.  Use the highest groove to level a bike with 25-28 tires.  Use the middle groove for 35 tires.

I'm getting rid of it because it takes up too much room and I don't plan on doing trainer rides beyond an hour and a half.  The real benefit of a rocker board is it reduces saddle hot spots by allowing the saddle to move a little side to side under you as you pedal, which I really start to notice at the 2 hour mark.

It has some chain fling-off smutz that will come off with a pass or two with a sander.  I'd recommend coating the top with urethane after that.  Comes with the Kickr Core mounting kit.  If you have a different trainer you can order mounting kits from Rockr.