We flew Southwest a few weeks ago with my 22 month old rear facing in her Britax Roundabout.
We had no problems installing the seat rear facing on the plane. The seat in front of her would not recline (at least not much), but no one said anything on either leg of the flight. I have always found when installing it rear facing that a belt extender doesn't help me and it isn't necessary to flip the buckle. I think those are maybe tips for forward facing.
I carried the seat over my head and down the aisle of the plane. I think it would be really hard for one person to handle both seats down the narrow aisles.
The length of the fixed end of the plane seat belt made it so that the buckle was sort of under her leg under the seat padding. This bothered her a little bit at first. We used a blanket of hers tucked under one leg a little to give her some relief or at least she thought it helped.
I'm glad to hear a positive story about RF an older child on Southwest, I was concerned after reading that a PP was forced to FF her 4 month old. I'm pretty sure that we will put her behind our FF DD, so we won't have to worry about the seat reclining. Thanks for the tip about the buckle, I will be prepared with an extra blanket for padding if needed.
