So we're back in VA and we did end up installing our Frontier on the plane (Delta airlines).
To transport the Frontier through the airport (since it's so heavy and there's no way I could carry it by hand for more than a minute) I fully reclined my Peg Perego Pliko Lite stroller and put the footrest all the way up. Then I sat the Frontier in the stroller facing out and secured it with a bungee cord around the shoulder area. This worked great since we had to transport the carseat from our car in the parking lot, through baggage check-in, and then through security and to the gate. And I was able to loop my carry-on bag (Land's End diaper bag) over my stroller handles so I could be hands-free. I also put Conner's carry-on (Land's End backpack) on top of the Frontier so he didn't have to carry anything either. At security, however, they did end up taking the Frontier off and putting it through the scanner even though I asked if they could just use the hand wand to scan it and the stroller together. They ended up hand scanning my stroller since they couldn't get it closed to put it throught the scanner machine and they wouldn't let me close it myself. The whole frontier plus stroller was a perfect set up, and at the gate I just folded up my stroller, put it in my stroller bag, and gate checked it. Then I carried the Frontier on board to install it by myself, while Conner and my bf stayed behind to board last and give me extra time.
For the install, I asked for a seatbelt extender just in case, but I didn't end up using it. Unfortunately, because of how the airplane seatbelts are, the buckle part ended up being right in the middle of Conner's back since the belt path (when using SBP) is on the inside of the seat, not the outside like the MA/BV/DC. The male part of the seatbelt stalk on the plane is extremely long (like 9 inches) and there's no way to shorten it like you can on the female end. Even twisting it wouldn't make a difference unless I twisted it like 12 full times and you're not even supposed to twist the male end! And adding the extender wouldn't make a difference since the extender has to hook on to the original male part and that would just leave you with a buckle both in the middle of the belt path and at the side. So what I had to end up doing (since Conner complained of the buckle hurting his back) is I folded up his sweatshirt and put it behind him in the lower back section so he could no longer feel the buckle. Now I know this is a big no-no in the car, but it's the only thing I could think of at the time and it was either that or not use the seat since Conner said it hurt his back. The only thing that would solve the problem I think would be if Britax allowed the Frontier to be installed using the LBP with just a lap belt. Then the seat belt portion would be routed behind the seat and the buckle wouldn't pose a problem. I did end up getting a tight install and Conner was fine in his seat the entire time. The Frontier didn't seem much wider than other seats. I wasn't able to put the armrest down at all, but my bf still fit in the seat next to Conner with no problem.
I'll try and post some pictures later.