You could probably use something like these:

https://smile.amazon.com/Reusable-Straps-Securing-Adjustable-Self-Adhesive/dp/B07CGSRN38/ref=sr_1_2?keywords=velcro+straps+1+inch+wide&qid=1674923526&sprefix=velcro+starps%2Caps%2C736&sr=8-2

You can probably find something similar at the hardware store.

What I would do is cut slots in the foam to feed the straps through, and then glue the strap to the foam from the underside, leaving the loop and the tag end of the strap sticking up. You may also want to get a lashing tab and glue them to the case under the foam to run the straps through, or, alternatively if you want max security, some low-profile strap anchors that you can then screw to the bottom of the case with some small screws.

Ex.

https://www.seattlefabrics.com/Lash-Tabs_p_385.html

https://www.strapworks.com/1-inch-black-plated-metal-footman-loop