In my experience there is no perfect luggage solution. Hard vs soft; loops vs throw overs; plastic vs aluminium; tote bag vs whatever. Each has advantages and disadvantages and different designs within each type have their own pros and cons. Best to work with what you have got, adapt it, add to it and work with it to make it suit you. Also adapt your packing, kit list and equipment until it fits.
For what it's worth I have an older model Giant Loop great basin. That is good but not without its limitations - mainly it most definitely is not waterproof and is a tad on the small side. I use light dry bags inside and have added a couple of bags to the daisy chains, and will also tie down something light on top of everything. I also add a tank bag and a couple of kriega US10s as tank panniers, along with some other small bags and tool tubes stashed around the bike for odds and sods. This works for me but is not at all secure - the biggest drawback of all.
Can't help with the specific question though other than to try USA based forums.
Sent from my iPhone with a smile