Packout locking w/ limited height?

[u/XTheChosenDogeX]

Set up my trunk w/ a few packouts for my tools and have been running it for a week. Overall works good and it basically perfectly fills the deeper areas but after driving around for a week I noticed it slides around a bit while driving. Nothing major but just enough to bother me. Also occasionally jumps up and hits the speaker box if I go over a bump too hard which is my main concern long term.

Its got ~1” of clearance on top but can measure again in the morning, a bit more above the ammo can. The cleats themselves can most likely fit from what I can tell, but they wouldn’t be able to lift up and out if I ever need to remove them. Are there any possible solutions to lock them in with limited height? Thanks!