If you fasten the straps to the under side of the seat you can then open the seat hatch.

 

I've done this.

Use the butt-stop positioning rods for the front tie-down points.
Use the seat bumpers on either side of the seat latch as the rear tie-down points.
May need to have a "permanently" attached (removable, but normally left on the bike) set of straps to which the bag is attached. These would connect the rings at the front to the loops at the back, with at least one more between where the rear loops meet the front-to-back straps, to pull them together.

Link to Thread: Passenger Seat Tiedown (Nothing Across Cargo Space)

Detail photos in Post #7

 

I have a pouch with is similar, and place it on the "Engine Hump" with the straps feeding under the front of the seat. When the seat is closed it is held n place with very little movement. I do have to lift my leg a bit higher to clear the bag, but 'so far' I still have the dexterity to accomplish it.
CHEERS

 

View attachment 103245

That fits very nicely, and you wont even feel it's there - a handy extra 15-20L right there

 

Yeah, but...whatever you can get in that, you could put under the seat.

 

Assuming the under-seat space isn't already spoken for...

 

I just ordered a 40 liter duffle bag. It measures 20" in length and is 10"x10" square at the ends. It should suffice for additional storage on my 650 Burger while doing lite road trips. At 20" wide its almost exactly the same width as the distance between the handrails on each side of the passenger seat making for easy tie downs. And with it being 10x10 square on the ends it will fit nicely between the "butt stop" and the passenger backrest and provide a little lumbar support as a bonus once its filled. Here's a link just in case any of you might be interested in one...they are less than $15 with shipping included!!!

Gym Bag for Men and Women, Travel Duffel Bag Sports Tote Gymbag,Waterproof Fitne | eBay

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www.ebay.com

 

Thats a sharp bag, looks like it's made for your bike. I have one that has been transferred from three previous bikes now and I love it. On the first bike below. They are great for your quick grab items, glasses for me, prescription sunglasses, hat, rain gear, gloves...whatever. Yes, the Burger has plenty of storage and compartments for everything, I was accustomed to using this on other bikes. Then one day my wife wanted to ride, and the bag came off. I easily found a permanent place for everything I had in my belove bag. The one thing I thought I could not live without was the spot to carry my water bottle, then I worked that out as well. I still like the bag on and using it would eliminate me from accidentally locking my keys inside and having Mikey ride up and do the emergency seat release mod.

I opened the seat, attach the strap in the opened position around the seat. This will allow the use of both your bag and the under-seat storage. After attached, loosen strap slightly so there is some play/wiggle room when closing, so not to damage the rubber seal.

 

Hey guys, thanks for all the feedback on my soft tail bag post. I had owned my 2023 Burgman 400 for about two weeks when I tried using one of my former motorcycle tail bags. I posted with the picture right after that venture. It's 36F in my garage today - a little chilly for my old bones; nevertheless, I got out there and tried using the under the seat posts of the backrest for securing the straps. Great idea which would have worked were it not for my straps being too short. Come warmer weather I may get longer straps and mount the bag to the seat rather than the handrails. For now I'm content to have all that great under the seat storage.