GO!! Have a great time!

My only suggestions would be that you pitch in and help out any way you can....... from loading things in the car, keeping the place your staying at picked up, not acting like royalty and expecting to be waited on but rather offer to get everyone a cold drink if your headed to the kitchen, clean up after yourself in the bathroom, etc. I think you get the idea.

I'd also ask him before you leave exactly how much money you'll need. I am assuming by inviting you he'll pay all your lodging and food. But what about sight-seeing, amusement parks, etc. Those things can run pretty high. Ask if you can pay your way to get in.