That's the best accessory!
I haven't read through everything either. When preparing for long trips start at the ground and work up. 1. High mileage tyres are not very forgiving and give a poor quality ride, compared with the better brands. I use Avons (Venoms on my old Glide) which are more flexible and smoother running. 2. Fit high quality shocks, to better smooth out road imperfections, which will further reduce fatigue and discomfort. 3. Only when those two are sorted should you consider a different seat.
Last June my wife and I went on a tour to Poland, covering 2,500 miles in just under two weeks. Part way through the second week she had had enough and was very uncomfortable. Spoiled the rest of the trip. May of this year we did a similar trip and mileage, with our new custom-built Ohlins shocks and the same Corbin seat (take note!). Comfort was never an issue and my wife declared them an unqualified success.
In other words, in our experience superior shocks will give the best return for comfort when riding long distances.