Looks like a nice bag. The only issue I might see is if you use it on the rear seat like you mentioned. The ends may "sag" a bit off the narrow seat and rub on the saddlebag lids. I've had that happen with a couple different bags on my '01 Police bike. Stiff bag bottoms are a must on those wide bags if used on the rear seat.
I have a couple riding buddies that use the old T-bags Dekker Supreme. Since '09, I've been using a used detachable Tour Pak (very handy) and a T-bag Dekker Supreme bag for the luggage rack on top of the Tour Pak.
View attachment 7033 The newer version appears to be similar.
http://www.jpcycles.com/product/800-069
It has 1" rigid foam inserts in the bottom, sides and top that are removeable. The bottom piece keeps the bag from sagging. Stiffens up the bag and protects fragile items like cameras and electronics. Plenty of room, especially when coupled with the Tour Pak!
It's around $200, but I bought one off eBay brand new for $100.
Even has two zippered on/off detachable "fanny pack" side wings for additional storage of items that may need to be on the go with you when off the bike (holster, phone, sunscreen, electronics, etc).
I use it every year for my Myrtle Beach bike week trip with plenty of room to spare (only pack for me, though).
Here's the newer version which is on Amazon.
http://www.amazon.com/gp/product/B0..._m=ATVPDKIKX0DER&pf_rd_r=00DXSZ2ZA8XW726Y9S09
View attachment 7034