Here's a few items I've played with, maybe they have some value here, use and improve-
I felt the tubes should be able to be secured- so I came up with this, for the standard tube and the long size standard;
Hardware used is 1" stainless d rings, 1/4" p clamps, stainless rivets, 3/16" x 1/2", and #10 backing washers. Fuel line bits are slit lengthwise, clipped onto d rings. They snug up the d ring, allow it to rotate, but also stay in place.
Here's the hardware I use for locking the Mega tubes. Some guys from Greece came up with a lock core installed thru the bottom of the cap end bracket, but the photo was too blurry to make out the exact arrangement. I chose this option to allow access from most any mounting configuration.
I use 5/32" stainless cable, swedged on 8 ga copper lug ends, and finished w/ clear heat shrink tube. Stainless loop attaches to cap w/ 3/16" ss rivets, backed w/ washers inside. Cable is anchored to tube vent hole, riveted from inside for smooth interior, and guided by 1/8" nylon p clamp on bracket. The 3/16 ss p clamp is installed on the opposite side as a parking spot for the cable and lock when not needed. The lug end hole is big enough for more standard size padlocks, I supply a basic brass padlock w/ my kits. Of any of the potential weak points of the design, it isn't the ss cable. I destroyed one brand new pair of cable cutters w/o evidence of damage to cable! The salesman first stated, oh yeah no problem, those are great cutters, to, "what a piece of crap" moments after I purchased and tested them.
One user pointed out the need for a grit proof padlock. So far I've worked w/ plastidip coating as a form fitting guard, still in beta testing. The pennytech fix is a fat rubber band fixed vertically across the key slot.
Happy Trails SU rack clamps, 7/8" p clamps, worked w/ vise grips and vise to squared off shape.
DRZ400s brackets- 1/8" flat stock, 1.5" & 2" widths. M6 bolt for threaded hole in subframe where helmet lock had lived, rearmost bolt at subframe attachment. There are better designs and executions out there, this was a quick design and build for a customer. I built another for myself, not yet tested extensively.