I am partial to the 3M Scotchcal material (xpel.com, or stonguard.com). I have the xpel version on my BMW and love it, expecially for those long trips that you are describing. Great protection for the entire front of the car and on the side view mirrors. It is a little pricey (depending on the car - $400-500) but well worth the investment. It will save you from rock chips, bugs, tar, etc. It is more of a permanent solution but you can take it off without any harm to the paint.
Check out this thread for some pics of some cars, including mine, with it on.
http://216.147.22.29/forum/showthrea...?threadid=3093