Attach the buckles using the supplied cable ties under the seat. The back cable tie goes through the loop furthest from the buickl and sits in an indentation in the rail. The front zip tie goes through the third loop from the back and sits just behind the end of the rail. Shown here using “practice” yellow zip ties for visiblity:

buckle placement

This will give you enough clearance to remove the tank bag without removing the seat. It might not look like it in this picture but you can grab the buckle with your hand:

buckle with seat on