I used small glue dots.
I stumbled upon a near-identical case at Mountain Warehouse today:
https://uploads.tapatalk-cdn.com/20180817/59f952246fcdb8e8671c16d3c03a6a10.jpg
https://uploads.tapatalk-cdn.com/20180817/cd211cefc24eb2a8830383450e8aa4dd.jpg
There are a few minor differences between this and the screen-used prop, but nothing that can’t be modified or fixed in due course. I also plan on repainting the case this week, and I’ve been on the lookout for a suitable Ant-Man figure. How do you guys keep your figures in place inside the case?