So here, what I do, is I have a strap that is about 10" long and has a loop on each end. I loop it over the lower triple clamp and around the fork (basically in a C shape) and feed one end of the loop through the other, then attach my tie down strap. I do this on both sides.
I set the tie down strap up so that when I tighten it, I'm pulling up on the loose end of the strap, as well as down on the bar on that same side, and go in increments between both sides to make it even. I doesn't need to bottom out the fork as that will end up blowing a seal during the trip.
So here, I attach my strap to the passenger foot peg bracket. There is a little hole in the flat piece that is perfect for the hook to go through.
I set this strap up the same way as the front. It just makes it easier to get it tight.
The bike will wiggle around with just the front straps on, but once the rear straps go on it will be rock solid.
You could also use this strap system without a wheel chock since the straps will pull in opposite directions, but I use the chock since it's guaranteed to work and makes it a job that I can do by myself in about 90 seconds flat.
I've done probably 30,000 km with my bikes tied down like this and have not once ever had an issue. My last trailer was only about 4'8" wide on the inside and they were always just fine in there too with no movement.