I created this holders for a 10L and a 12L scuba tank.
- 2 holders per tank
- 1 wooden board
- 2 tensioning straps (I bought them at IKEA)
- 8 screws and nuts (M6)
You have to keep the tensioning straps tight for secure transport.
Beside of the material above you have to think about how to fixate the wooden board in the car. For it works perfect with a rubber pad and to put the board in a corner of the boot, but don't blame me if it is not working for you.