I bolted the front stabilizers to the front edge of the steel floor of the front storage compartment. Works fine. Mounting the brackets at the front bent edge of the steel floor provides plenty of support for the struts.
For the rear, I have an enclosed underbelly, cannot see what is under it, and did not want to take it loose or cut it. So I added a piece of 2" x 2" square tube from one side of the frame to the other, and bolted the strut mounting brackets to that tube. Very sturdy. A metal fab shop could easily make one for you.