I have 2 old SATA SSDs laying around, and wanted to use them with the Pi 400 in the Pidock. Sadly, they're far too large to fit under the Pi in the tiny space where the cables run. I've never opened an SSD before so figured I could try to fit the bare board. I didn't have the right screw driver, so I used a tiny flat head to get one out, then tore the case apart after peaking inside to confirm it would be small enough. I was surprised at how tiny the PCB was, and quite happy. I threw the mangled case away. I'm able to fit the board nearly under the Pi, and may be able to find a SATA to USB adapter that will fit as well. If so, I'll have a SATA boot drive tucked neatly underneath the Pi in my little laptop. It still takes up a valuable USB 3.0 port, but I find the added responsiveness and reliability well worth it. After the Pi corrupted and destroyed my 256GB SD card, I'd had enough. I'm currently booting from a 32GB Samsung Bar flash drive, with a 32GB SD card used to hold TimeShift backups. The otherwise unused SD slot has been great for just adding extra storage. I plan to add a 512GB SD card for media and backup storage, and will carry extra cards to swap out as needed. I'm currently using a 256GB Samsung Fit Flash drive to store media, but it's already full. Once I buy a new laptop and compress all my media, I should be able to take my entire collection with me. 

I took a few pictures as words don't do it justice. 

I hadn't considered doing this until I started researching USB M.2 drive enclosures,and realized that I have SSDs laying around. I need a SATA SSD to USB adapter for data recovery as it is, so I'll just make sure to get the smallest one I can find, or one that can be trimmed down easily. I may even be able to get 1TB+ drives that would fit in like the one above. I'll order the adapter sometime next week and get it set up. May also order cooling fans for the Pidock. It needs a little help.