I'm not sure how they would work without an E-track
E-track is the easiest, but if you always trailer the same car, and stop at the same spot, then three stationary anchors per wheel will work just fine.
I like E-track since it offers flexibility (for different vehicles) and maybe more importantly, because it can be fastened well to the trailer. And with the tires sitting on top of it, that also helps.
On this trailer there are crossmembers every 12 inches, and the extruded floor panels are fairly stout, too. That allowed me to use two bolts per foot, then rivets in the holes between them. No need for backing plates in this case.
On this little open trailer I could put bolts every six inches, so it was well secured, but the L-track isn't as strong as E-track. It was okay for the small and light cars I used that trailer for.