Don't know what bike you have but I used a krauser when I had the 1150 adv. Sorry can't remember the model but it could handle 2 lids and was very light, waterproof and easy to fit etc.
Hepco and Becker are the only makers to retain the grab rail on the standard 1150GS- got one of their largest ones and am very happy with it. It looks a bit smaller from the outside than a Givi Maxia, but I cant believe how much it swallows.
They are also reasonably priced- got mine from Motorworks when they were having a H+B sale.
I have had a Kappa (45lt i think) top box now for many years and 1000's of miles, plus a few offs.
It has done me proud, no leaks or faults. Fits a standard Givi top plate. Alot cheaper than Givi when i first bought it and if i remember rightly Kappa are made by Givi. Fits two helmets easily
Yeah, the point I should have made clear was that you should make absolutely certain that the box does what you expect. 46Ltr capacity might imply that a helmet (or two) will fit, but it is entirely dependent upon box model and helmet type.
I also have a Givi (E52 Maxia) and it's been great. I got this one specifically because it holds 2 System 4s which are bulkier than ordinary full-face. You can get both helmets plus gloves and other assorted goodies in easily. Cost around 200 quid for the box and 12GS plate with a next day delivery from Calamander.
go on e bay put in motorcycle accesories, then put top boxes in search, loads different size chinese copies of givi, i got 45 litre and plate for less than 50 quid, good product as well
Been using a Givi E52 Maxia on my 1150gs for the past three years .No problems with the box or carrier in that time but it is on its second lock set, the keys are made of monkey metal and bend & snap quite easily.You can't buy replacement keys so its £15 for a lock set.
Other than that a cracking bit of kit, it will easily take 2 full face helmets and doesn't affect stability on the bike.