I use either industrial/outside rated velcro or 3M double stick tape. Velcro is thicker if your short on head room, 3M tape makes it a PIA to remove anything.
The theory is that the enclosure is a shield to protect your components, not a structure to hold your components. That being said, I have built boards where I mounted everything in the enclosure and then bolted the enclosure on. In practice its a lot easier to work on a board when you can remove the enclosure and all the components are in place.
For thinks like charge ports and volt meters that normally get mounted/recessed into the enclosure I use quick disconnects so I can fully remove the enclosure.