I have both the 15' and the 10 ' extension and they will not compact enough in the standard bumper
Been there tried that!
My solution was to purchase a Vinyl 5"x5" x 8' fence pole and two end caps from HD
Bolt it under the frame in a convenient spot.. My new trailer has the sewer connection in front of the wheels. Use a couple of rubber Tarp straps bolted to the sides and end of the end caps Instant storage for the stinky Slinky!
I store the extension in the bumper
The 15' in the Pole and handy for normal use
I intend on getting a hard plastic sleeve for inside the bumper to ensure rust does not poke holes in the extension which I hope not to use very often