I've got one of these:
https://www.amazon.com/dp/B075B6RVYW/
In addition to the adhesive backing I drilled the supplied screws into the interior plastic trim to secure the mounting points and have had no issues with anything coming loose.
Most of the time the bottom stays attached and I keep the top detached and stowed under a weathertech cargo liner. It's been handy and is certainly cheap enough.
can you post pics of how your mounting points turned out?