Can fit it behind (alloy) pannier with P clips on GSA. Secure but still accessible with panniers on. Here's mine on hexhead but friend has his in same place, other side of course, on his LC.
If you feel the need to lock your tooltube just put a small black self tapping screw through the top and the thread (but keep a suitable screwdriver to hand!!)
Not sure think it was 20mm I was scratching about in the box of " that will come in handy" bits and used them along with a bit of alloy flat bar. Been on for last 40k miles and no problems catching wheel and once pannier on difficult to see.
PM me your details I have a box full of Pclips can send some over
I used a Torx security screw to secure mines. Just tighten the top, then drill a small pilot hole and screw in the self tapper. Remember to put the screwdriver into your tool kit