The tilting frame sounds like a great idea. Unfortunately that is a little too much for my skill level.
I am happy with the finished product but the proof will be in the pudding.
I ended up sticking the eye bolts right in the middle of the tool box. One at the rear of the bikes, one in between both and one in front of both.
When I stuck a bike up there and tried to hold it down by the handle bars it still had a bit of wobble about it. When I held the bikes in the middle it seemed to reduce the wobble. I intend on using a cam buckled strap to hold them down so as not to rip the eye bolts out of the toolbox with a ratchet strap. I did use a length of 3 mm gal on the underside of the toolbox to spread the load of all the eye bolts across the width of the toolbox.