Daniel Dirt used to make 'o-rings' out of silicone fuel hose to strap his tanks in, but I think also had a "ledge" to support the tank and used shims to adjust tank height. I don't recall how he did the joinery, but no knots. Neoprene O-rings might work with some planning and the "ledge" plan. Our NW Profile Stunt rules would allow incorporating a pair of plywood ledges into the nose/wing joint structure to both stiffen the nose and also support the tank, with shims top and bottom to adjust height. Worth a thought.
Few are as observant as Steve, but it has been a while...
I would use bands made from silicone fuel line to hold tanks in my
Impacts. Cut a length which looks right. Join ends by sticking a 1 1/2" piece of all-thread rod (4-40) in each. Wrap with serving wire to create quite a strong loop. Never had a failure but still I would use two of these loops.
With the
Wimpact series of profile models standard "O" rings from Local Hardware (McLendon's here in the NW) were very effective, along with being neater and more reliable than rubber bands of any sort.
There was no actual ledge for tank to sit on, although it sure would look like it with model sitting in pit area. Instead, tanks would sit on shims between tank and bracketry, said pieces not being moveable. This was quite handy as shims were also used on top of tank, although each shim stack contained various thickness shims, from 1/64" to, well, much thicker. The handy part came in when needing to move tank up or down that magic 1/64". One could remove appropriate shim from, for example, upper shim stack, slip it into lower stack, strap tank back on and go fly with confidence in the adjustment. And no lost shims or confusion.
Dan