*Most* of my 500 mile days were on the TLR, including the Iron Butt I knocked out in May. It's seating position isn't what I would call a couch. :redflip
Since you've never done a ride that long before, I'll make a couple of suggestions.
When you stop for gas, knock down some water and a granola bar. It will keep you fresh.
After you gas up, take a few minutes to stretch your legs, your arms, roll your neck around a little. Should help keep some of the cramps at bay.
Good luck and have fun ! Hitting the highway is a blast. It's relaxing and therapeutic for me ! It gives me time to think and clear my head. I'm ready to do it again.
Edit: If it takes you 9 hours to ride 380 miles, you're riding too slow. I can do all of the above on a 500 mile trip and make my destination in 7 hours or a little less, and that's not busting the hell out of the speed limit either.