Here's a pic of my typical "Packmule" setup
Givi soft bags, don't know the model. It uses a sort of "mounting pad" that attaches to the seat with straps. The bags then attach with quick-disconnect buckles. Something like ~$65 used.
For the upper, I obtained some "Mal~Wart special" backpack/rolling luggage-thing, with an integrated frame, ~$15.
Finally, a Marsee magnetic 20L tankbag ~$145 (the only thing I didn't obtain second-hand or on clearance). Total weight of all the "packaging", including bungees is probably 18-20lbs.
Also pictured are a 4-man tent (red bag), a brown/silver 8'x10' tarp I use as the groundcloth (modified so I can stake the tent through eyelets, and have a "porch"), and a Coleman sleeping-bag, secured through the "slings" of the backpack. Not seen is the full-size air mattress and inflator, or 5 days worth of clothing, and other assorted "gear", including a laptop, variousl tools (or which I've had yet to use for myself), .22 pack rifle, .45 pistol, and ammunition. (it's PACKED, dude!)
Altogether, about 105lbs of "cargo". Substantially less than a typical passenger. And *IT* doesn't move around, or lean the wrong way in a turn.
I used an abundance of those "flat" bungee cords, with the reinforced-plastic hooks, in assorted lengths (I stay away from those metal-hooked POS things, I've had a high failure rate with them. plus, they scratch every damn thing). If one looks even slightly frayed or like the elastic is "breaking" - I toss it. Carry spares, it's easy to have a failure out on the road.
I like the Givis a lot more than I thought I would at first. There are several "D" rings at strategic places on the bags, they allow extra places to attach bungees.
Heavy things go low, things you might have to have *right now* go in the tankbag, or on my person. Always distribute the weight evenly from side to side in the saddlebags (like I need to actually say this).