Best seat pads/covers

[Grumpy Goat]

... I've never ridden more than 400 miles a day let alone for days on end.

What are your best suggestions for pads or covers to ease this 56 year-old's posterior's possibilities?

Depends what the specific needs are. My suggestion is always to test ride the standard seat for the desired duration and see how you make out and what your needs might be. I have 6 years on you and can ride 500-mile days back-to-back. It is not like sitting in my armchair of course but the discomfort is not enough to make me want to get a different seat that cups your butt and stops you from moving about. The RSs seat is fairly comfortable to me and if I stop every 2 hours, I find it is comfortable enough.

That said I do have a seat cover on the bikes, and it also helps with cushioning in addition to its primary function - heat dissipation.