Do some dry runs. Get all your stuff packed into your panniers and/or trailer, and ride for a couple of days doing your intended daily distance, or try to set a slightly easier goal like between 30 and 45 miles. You should know where you are at after the first day, and by the second day of riding that same distance you will become more confident about your riding abilities. Try to pick a route or two that includes varied terrain and road conditions--maybe a rail trail, a service road, small town roads, downtown roads, a rolling back country road, etc... Good luck!

I just did a 50 mile loop yesterday and a 40 mile loop today on different roads with different grades, and I'm feeling a bit more confident than I did yesterday (since I've been off my bike for a month now due to injury), but I'm back in training mode for my tour! I'm planning on doing at least 30 miles a day for the next two weeks prior to my tour.