I was just looking at the gaps to the outside of the boot. Just as an outside the box suggestion ?
We filled in a couple of the gaps using large tupperware like containers. These contained all the computer PSU/camera/iPad things. When we arrived we simply took out a lightweight nylon (think parachute silk) sports holdall and put all of the smaller boxes into this for convenience. When empty the holdall folds to nothing and rested on top. A little bit of velcro held them all in place (about as much as the panels they were attached to anyway)
https://www.amazon.co.uk/BagBase-Shoulder-Sports-Colors-Black/dp/B00I64GIIKhttps://www.amazon.co.uk/LEGO-Brick-Knobs-Stackable-Storage/dp/B003NE5L9K