Tailpack for a Helmet?

[Nomad Z]

Any suggestions for a tailpack that can take a full face helmet, and can be taken off the bike for carrying around? Budget up to around 50 quid. To fit my Gladius, preferably onto the grab rails - not into taking the seat off (I already have a Scottoiler and reservoir under there, and would rather not faff with getting straps under as well).

Looking for something that I can use as a bit of soft luggage in general, and for making the helmet easier to carry if I'm off the bike. Prefer carrying as a shoulder bag than a backpack. Waterproof would be good, as would some sort of pockets or compartments for bits and bobs (such as sarnies, drink bottle, map).

Two that I've seen are one branded MotoGP, and an Oxford one. Not sure of the features yet, or the build quality. Are they any good? Any others to consider?

[Chuffin Nora]

https://ecx.images-amazon.com/images/I/41IocHBMRPL.jpg
[Other brands available]

Also known as a roll-up top box.

Several advantages:

When not in use i.e. when rolled-up and bungeed to the pillion seat, it doesn't spoil the lines of the bike like a top box does.

Walking about town with [your lid in] it looks like you mean business, packing, loaded for bear, and not some schmuck lugging around said (cumbersome, oft awkward to deal with) lid.

If it's big enough it'll hold half a week's shopping/half the dismembered remains of yer average pikey on his way to pushing up the pine trees.

Because you've always got your 'top box' with you it aint gonna get broken into.

Generally not at all waterproof, but nothing that a bin liner wouldn't solve.

Sorted.
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There's a fine line between integrity

[Northern Monkey]

The come in waterproof versions as well

https://www.blacks.co.uk/equipment/143964-berghaus-global-40l-holdall.html
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Fisty: after polishing the tank with the glistenng beads of sweat from my full hot scrotum, I filled the headrace bearings with 10cc of my manmilk

[talkToTheHat]

Consider a 30litre or larger rolltop drybag. I have a held one. Lomo make them too. Can fit lid, gloves, trousers and back protector in my 30 litre one.

Affix with rok straps. They are a little stretchy, adjustable, and have soft fabric ends that don't chew paint. I have a pair under my seat for random awkward cargo.
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Bandit. does. everything.