I’ve got one of those and I think you could probably gate check it plane-side. You should be able to get it through security since it is utterly non-dangerous. My only concern would be someone ripping the bag, but you could protect it by plastic wrapping the whole hoop area before going in.
Just confirming, at least on Southwest out of Atlanta and back from Denver, that I was able to carry on my Fishpond Medium length (37″). I have one of those Fishpond sling packs that has the slot for the net, so I just left it in there and walked right on. I pull it out to fit better in the overhead bin, but no troubles at all. It was more of a talking piece than anything in the airport, haha. Security, Flight attendants.. They were really just interested. I also strapped my rod tube to the sling pack. The whole thing counted as one carry on. I figured it was one of those “ask for forgiveness” kinda things, as they’d gate check it at worst.. (My buddy did the same thing, sans the sling pack, by strapping his to the Orvis rod case.)
I would highly recommend checking with the specific airline you will be flying with ahead of time…… A lot of things that TSA will allow you to carry-on may not be allowed by the airline.
I had a bad experience recently trying to carry on a rod tube while flying Frontier. They did not allow it being strapped onto my pack to count as part of my one carry on. Ended up paying $40 to check it.
In the alternative, you might consider mailing your gear. I mailed my stuff to my rental car company on a trip to Bozeman a couple of years ago (shout out to the amazing Phasmid (now Explore) Rentals out there). Hertz probably wouldn’t take it but a local fly shop might. It allowed me to bring a couple of rods and a little more gear than I otherwise would have while being cheaper than if I had to check it.