I used a Corbin for about a year on my bike, until I could get a Muscle Seat. I liked it just fine. I'm 6'3", and at the time 275lbs (225 now), and found the wider, taller profile great on long trips. I've done 1000 miles + in under 48 hours on the bike twice, one with the Corbin and one with the Muscle Seat, and I think the Corbin was the more comfortable seat towards the second half of the ride, while Sean's is definitely more comfy during the first half.
I had no problem with the filler-cap issue, because I didn't use it! I bought the seat used from Sean, and it didn't come with the bolts to secure it to the frame. I asked Sean about this, and he said he didn't use them, so I figured I'd try it his way and I never bolted the seat down. I just took the whole thing off when I fueled up. On long trips, I even ran bungees through the hole in securing my bag to the seat, so when I took it off the bag came with the seat. Took maybe 3 seconds and was as about as hassle-free as you could want.
It's definitely not as pretty as the Muscle Seat, but it does give a little extra leg room for those of us with longer inseams.