I have never driven my M3W in the rain, but have made number cross country trips by motorcycle. One suggestion, put your rain gear on and go out in a real rain storm and try it out. Something as small a a drip down your neck or a leaking crotch seam will turn into a Chinese water torture over the space of a few hours. Best investment I have made is a premium Gore Tex Pro suit and a quality full face helmet. I also agree with PaulV suggestion on a good roll top dry bag. Of course, you could try not to drive in bad weather, but that can put you in a motel for days.
I-40 is about as good an Interstate ride as it gets! You will read on some sites that the road surface (in areas) is deteriorating, but I didn't find that to be the case two years ago.
Final suggestion- When planning your trip, account for break downs, side excursions, etc. If you try to tear across the country like an over the road truck driver, you will miss so much. Nothing better than those unexpected stops at road side what-evers, to make the trip memorable. Seeing those private tractor museums, worlds largest ball of string, etc, will make the trip. And try to always eat at a local restaurant. That's where you get the real feel for the area. In a local diner, you will meet the most interesting people and have the greatest conversations, which is what it is all about! Take lots of pictures and keep a simple diary/log.
Thanks for the tip & encouragement on the I-40. I feared it might be too straight and boring of a drive as I stick to backroads and old highways around me, but I can't afford more than a few weeks for this trip. Looking forward to it and all the side excursions.
I'll keep a log, take plenty of photos and possibly add a GoPro to the trip. Roll top dry bag is all set - I'll consider some quality rain gear next.
