I have used over winter an Oxford X30, don't know if this will be to big for what you want it will expand to fit a helmet, I have it small sandwich and drink for work, have had no problem with it sticking in place with only 4 magnets, at work I stick it with only 1 flap 2 magnets to the lockers and if I try pulling it the lockers move, have ridden without header strap as well, no leaks all good