My straps are 2" wide.

One foot of standard Vecro 2" wide on the free end of the strap is more than adequate.
I would steer clear of molded plastic Velcro style fasteners, and use regular cloth backed non-adhesive Velcro, because you can sew it onto the straps with a standard sewing machine.
That's how mine are made.

Here's how I did mine:
As I mentioned earlier, my shelves are 8' x 8'.
The strap only needs to reach across the airplane from one end. The opposite end only needs to be long enough to hook onto the other end.
My rear straps are about 8 feet long, and the forward straps are about two feet long.
From the rear end of the trailer, pass the strap over the airplane, and slip a foam pad under the strap
Do this for each side of the airplane.
From the front of the shelf, draw the strap tight, and press the Velcro covered strap ends together. Do not overtighten......the weight of the airplane compressing the 2" foam rubber will help keep it from moving.

On my last trip, I carried five jets. I had two of the airplanes strapped down, and the other three were just sitting there.
None of them moved at all.

I live in an HOA, and their ridiculous rules force me to move my trailer to a storage facility during the winter months. I'm bringing it home Wedensday afternoon, and will photograph the straps for you later.