Ok, this is coming from someone that's made that trip and has made numerous numerous 2 hour "rides" just to get to the meet spot for a ride. Honestly the "I have never really ridding in one direction for more than 2 hours?"" concerns me, and probably anybody else that would be leading a group down to the GAP. But that's OK, I was there too. Get some more miles at one time under your belt (I was told this when I first started riding with the Core group of riders on here.) so you can judge things like; mileage at certain paces (not what you've read online or in a magazine in terms of mileage), what pace can you consistently and safely run all day? Safe being the key word. How long your ass can handle the saddle without needing a break? How long should you ride before taking a break before you actually need one? Doing that will also kind of give you an idea of what potential modifications you may need to do to your bike to make the trip more comfortable, whether it be a new seat, bar risers, etc.
Roads down there are nothing like they are up here, in the best, more exhausting way. I'll tell you that while I completely and thoroughly enjoyed the ride down there, I was physically and mentally exhausted from all of those sweet sweet miles. Ask @Tpoppa as he had to baby- lead me into the Gap after back to back 500 mile days to get down there. (That man is a machine.) I had to slow my pace way down not because I was physically exhausted, but because I was making mental mistakes on easy shit.
More miles more miles more miles of the good stuff aka twisties will better prepare you for a trip like this. There are plenty of guys that put down more miles than me a year on here and I'm sure they would be more than happy to share their feedback too.