Those simple holders may be applied to your trunk floor using velcro. They will then keep things in place and ensure nothing is flying around in your trunk.
The model is intended to be used with 2cm wide velcro. You should be able to get this anywhere - mine is just bought from Amazon.
About the holders: The plain one is just a “L” shaped object you can use to keep things to one side in your trunk. It has a big base so it holds stuff tightly. You may also push the base under your things, this way it should be even more sturdy - at least for heavy stuff, as its weight will ensure the holder does not rip off.
The hinged holder is to keep things into the edge of your trunk. This is especially useful for boxes of any kind. The hinge itself is pretty robust so it won't break when you rip the velcro of your trunks floor. As it should be used in an 90 degree angle the base can be much lighter, due to the 90° bend it will still hold things nicely.
Both holders have a 0.5mm deepening so the parts will not pivot over the velcro too much. Also the printing orientation of the parts ensure the holder itself has a good layer orientation, so both should not break easily. 💪
Note: Please do NOT try to print the STEP files directly. At least Prusa Slicer will do strange things as I kept some parts separate to allow for easy changes. This causes the slicer to try to print individual bits, that are touching each other, which may lead to print failures (I expect, have not tried it). So when printing use the STL files. Still I wanted to also provide the step files so you can more easily change this to fit your needs. So if you want to remix this, feel free to grab those STEP files. When just printing this, stick to the STL files. 😉
Printing instructions: Print however you like. Just note that PLA will be to weak for the temperatures inside a car, I suggest at least using PETG, better use ASA/ABS.
And as said above: Do not use the STEP files for printing (see note for details).
Similar models: After having this model done I discovered that there was a Transportation contest some time ago. A similar model did win back then, see https://www.printables.com/model/138421-car-trunk-fixing-element-velcro for details. Shoutout to the author of this. If you look for a aesthetically more appealing model maybe try this instead. If you want a hinge, use mine. 😇
The author marked this model as their own original creation.