Hey (B)Eagle!!
I have always found Mustang touring seats to be good in the long haul.
I have not had the pleasure of trying the "Road Blimp" but it looks like it should do the business - at a price....
Are you planning solo rides or with a "naviguesser" (thanks, whoever, - I love that word)
Either way, what you are going to need (more than just a comfort cushion) is a good (adjustable) backrest - this will make all the difference to your back (and general upper body well-being) on the extreme runs you are looking to undertake.
Problem is, a comfortable (for you) backrest tends to get in the way of your pillion's comfort, so you will end up making lots of (= too many) stops which pretty much precludes really long trips (and stable relationships - been there - done that...)
So what's the answer?
Well, I dunno.
You, on your own? - with a backrest and firm buttock support = Corbin solo?
With a co-pilot? - a good dual = Mustang (IMHO) - hard to beat.
Or travel in luxury (I imagine) and go for the inflatable Zeppballoon.
Let us know which way you decide, and enjoy the long trips.
Best Wishes
Dave