My experience with a 2014 HW 277...
The tent end hoops had sockets top center. Those sockets received a plain-end of the tent support that connected to the ceiling in the cabin. But the pipe had a bit of a shepherd's hook on the end to engage a multi-step clip mounted to the ceiling. So your pole does not appear to serve that function.
If it were an awning pole, there would be two of them. Not only that, but awning poles in bag awnings all nest in the awning frame at the end of the awning. And they need to be adjustable.
If it were a bed end support, there would be two of each size. and they would be much sturdier...no slip joint in the middle, because the beds are heavy...especially when loaded with people.
I don't think it's used for extra support for the canvas on the slide, because of the sharp plunger end...and the main canvas support also goes into a socket on the hoop and has a shepherd's hook on the cabin end.
So, with those things ruled out, one option comes to mind...but it's a stretch. Is there a soft "tee" end that this might slip into? I ask because I ended up buying
a tool to help tuck the canvas. I'm 6'6" but we lifted our rig for boondocking, and this made tucking the canvas a difficult chore. My "rug rake" handle extends, so I could tuck canvas very easily from the ground, rather than climbing on the A-Frame or rear bumper and putting my body under the partially closed roof. I highly recommend this tool. The first time you're tucking wet canvas in the rain and standing on the steel bumper or A frame...wondering if you'll slip off and break your neck...you'll be glad you have it.
If you don't have another part that snaps onto that pin at the end of the pole, my hunch is that the pole was added by mistake. Just a mistake in finish assembly.
Obviously, things change in 9 years, but I'm not aware of any tent-end pole on any PUP that doesn't have some sort of shepherd's hook on the end to engage the bracket on the ceiling inside the cabin. And the cap on the end defeats that purpose anyway.
Sorry I couldn't be more helpful about the mystery pipe.
P.S. If you plan to boondock, this rig sits very low. I lifted mine because I smashed the stairs over and over again. I installed the torsion axle lift kit, fixed the stairs, and never grounded them again. You might also want to support your freshwater tank. Pix show the stairs (pre lift), the fresh tank support that's an easy add on this rig, and the same photo shows the lift kit on the curb side of the rig. That goofy looking support is just 3/4" galvanized water pipe, plywood, and a rubber floor mat, but it worked great. My first fresh tank developed a big crack from lack of support. If you have the same "looms" for routing propane plumbing and other features, you might be able to replicate.
Also, if you plan to boondock...dry camp...let me know. I had a great basic solar setup on my PUP, and, with judicious power use, I could go to bed with a fully recharged battery each night...without using the generator except on rainy days.
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