I took a page from Erik and I now hold everything in with velcro. They have this blue velcro at Hobby king that's incredibly strong. This is the stuff

https://hobbyking.com/en_us/polyeste...rong-1mtr.html

I know guys that put a large piece of the loop right down in the bottom of the tank, like wall-to-wall carpeting, and it works great. At first I found it hard to believe, but after trying it for myself I've found that whatever I put in with this stuff (smoke units, IBUs, receivers, speakers, whatever) it's not going anywhere.

For rotation motors and more permanent items, I drill and tap wherever I can. An M3x0.5 tap is a very valuable tool.