Oh, and Tristan, I had a dual sport bike, Yamaha WR250R, a friend with more trail riding than I told me this trick one day when we hit a trail with a lot of muck and sandy parts. It made a HUGE difference in the ability of the tires to grip in the loose stuff. When you are going to do long stretches of road that you wouldn't drive a car down, and you won't be going over 25 MPH, lower your tire pressure to about 18psi. It will make the grip on loose surfaces amazing. You will have to get a portable pump that attaches to a powerlet or SAE connector so that you can pump them back up when you get to a road.
I am only telling you this because you mentioned "400 miles of dirt road". You might want to invest in some good boots if you don't already have them. You won't need motocross, heavy, articulated armor things... but something that will protect your ankles, calves, shins etc. When "kicking-off" of stuff you will bang everything below your knee on parts of your bike, and bang your toes and ankles and heels on stuff. The boots usually have a reinforced shank too, so that you can stand up on your pegs without killing your arches.
These are really stiff at first, so you will need to break them in before your trip. Take them for a good hike up a hill to get them flexible.
If you have a pair of boots that come up 3-4 inches over your ankles and they have a good toe box and heel cup, then you don't necessarily have to have "motorcycle" boots. but they need to protect your ankle/shin/toes/heels from banging on footpegs and rocks, allow you to stand on the shank in the sole without flexing too much, and give your ankle some support.