Thanks for all the replies!
My bike is an SV650, so there's limited rear seat surface area; I could theoretically strap my rig down long-ways (as opposed to across the back) in a bag, with the helmet bungee-netted on top of that.
Alternatively, a side-ways tail bag could work if it's big enough. I'm looking at this bag from Wolfman: http://wolfmanluggage.com/products/beta-plus-rear-bag, but I'm worried it will hang down too low and contact the tail pipe - no bueno.
For those of you suggesting actually wearing a bag on my back, it sounds like the right move is to put the weight on the seat as opposed to the shoulder straps, right? If that's the case, is the fact that the bag is then looser not an issue w/ shifting around? I have a great backpack that fits my rig and it has a waist strap as well that I use when traveling, but a) I'm an hour and a half from my DZ and b) I'd be worried about the bag shifting weight around unless I tightened the straps (putting the weight on my shoulders, and probably leading to some discomfort after an hour+ of riding).
As for a BASE stash bag - having done my fair share of hiking with one on my back, I think I'll avoid that. They definitely shift around, and those straps are not built for comfort, that's for sure.
Thoughts?