Okay, thanks for the advice, guys. I'll probably follow mups suggestion with the flathead bolts.

We shouldn't forget that velcro does wear out and will require service, eventually.

The end corners are each held with a lap and a half of double sided velcro around the cross-members. The tray has a spine that runs lengthwise and locks into a built-up slot on the face of the cross-members, so it can only be extracted straight up. I pull-tested this to a few G's, but not to destruction, of course.

The batteries are held to the tray by surface velcro longways plus two double-sided velcro straps crossways for redundancy. I borrowed this method from JAS and it's worked well for me for many hundreds of flights. I'm not changing this part.

My previous two electrics have been conversions and this is my first one not designed to be oily. So in the past I've simply strapped the batteries down to a pipe floor rather than deal with a separate tray.