I set my Kauffman up when empty on the truck the deck right behind the neck was 1-2" above the deck in between the trailer tandems. When loaded it was 0-1" below trailer tandems deck height..
Another point of reference.. Leaf springs on the 10 and older trucks seam to have a sweat spot with top of the truck frame about 31-32" off the ground with 32" tires. Puts the OEM bumpstops about 2-3" off the axle. Truck is loaded enough to fully work the spring without bottoming out or bounce off the overload spring on the bottom of the spring pack.
Seam like you got enough straps on there..
If you prefer straps... Look into wheel straps that go over/around the tires..
I prefer chains. 5/16" grade 70,(4700#wll) with lever/ratcheting binders.
1-20'
2-10'
4-binders
Would be plenty for one truck and allow you to have 4 point securement.
Swing by Lowe's/home depots see if they got some scrap carpet in carpet area, put it between the straps and steel.. It will help protect the straps. Probably find some rubber/carpet throw Mats at like dollar general/family dollar/dollar tree they usually sell them in a 12" x24" size for 1-2 bucks. Cut them up in strips to use to protect the straps
I was planning on using chains around the rear axle but with the brake lines and stuff there is no good spot to put them without messing shit up. Good idea on the carpet.