Like the other posters have stated, you don't have to be a mega athlete to go on a loaded tour. I was mainly a commuter cyclist before I ventured on my SF to LA trip down the Pacific Coast. I addition to my daily short commutes, I would a 40 mile loop once a week for a month leading up to my trip and one 50 mile loaded practice run a few days before I was about to embark on my tour.

I clearly didn't train enough. It took the first four days to feel solid on my ride. That's not to say that I was in extreme pain for those first four days. I have great memories of the first half my tour, but I probably felt a little discouraged at times. The biggest breakthrough after those four days was mental. Once I stopped obsessing about miles completed, mph, and making my destination in time, my enjoyment of the tour increased exponentially. In addition to not looking at my bike computer every 5 seconds, I learned to relax into the climbs. I just stopped anguishing over big ascents, and, instead, dropped into my granny gear and soaked in the scenery. It was at that moment I fell in love with touring.

I would suggest that you get accustomed to long climbs. Learn to like them. Also, give yourself a couple extra days so you don't feel rushed. There's plenty of campgrounds along the Pacific Coast, so if you feel like you can't make your destination for the day, you can always find another campsite along the way. When all is said and done, your body does what it has to do.

Have an awesome trip,
Tom