Tell your son to have faith in his (and yours, and his brother's) abilities. When my wife and I left on our 2400 mile loop through the midwest last year, I had exactly 54 interstate miles on my coupe. I had been putt-putting around town for a year, but had never taken it long distance at highway speeds. We made it with no complications...

I just saw a weather forecast: upper 70's with only 20% chance of rain all next weekend. It should be perfect roadster weather.