I have an old ECLIPSE tank bag i've been using for many years.
It has a universal front harness that goes around the neck of the motorcycle,then has clips to the front of the bag.
The rear has a strap that fastens under the seat & clips to the rear of the bag. Unfortunately the rear strap cannot be mounted on the 1800 or the 1500 either for that matter.
I just secure the rear of the bag with bungee cords to the rider foot pegs, & unhook fromt the top rear when gassing.
The bag has a foam pad on the underside & hasn't scratched my paint yet in over 25 yrs. of use on 6 different motorcycles.
Bag has a large,expandible center compartment, 2 side pockets. Doesn't interfere with steering, & comes in very handy. I can pack enough clothes for a week with this bag alone,excluding jackets & rain suit.
I bought a new TourMaster magnetic for my VTX before I left for Pikes Peak, and found it perfect. The first thing I did when I got into Colorado Springs was to go to a bank and get a big cash advance, all my credit cards were useless in a scanner. The directions say not to put anything like credit cards in this tank bag, and now I know why.
I,ve used an eclipse on a 1500 and my 1800 with some degree of sucess.
BUT,be patient.I was at the "Electrical Connection" the other day and Lewis showed me a tankbag he was developing for the 1800.Looked pretty slick.