Secure stacked vehicles together first before beginning the stabilization process on either of the stacked vehicles.

The Basic Stabilization Steps

Support the high end -- secure to the frame or use a chain

Start with the struts at a 45 degree angle -- you need to end with 45 to 60 degrees bottom angles

Secure the base-plates and tighten -- lifting slightly as you tighten the lateral supports

Photos from Rescue 42 training materials located at 

You should watch the entire video.