I traded in my vstar 1300 for a 2014 Road King while on my way home from vacation in the Smoky Mountains 250 miles away.
Left the 1300 at a Harley dealer in Pigeon Forge, and drove home on the new Road King right from the dealer with my wife and luggage on the back. 250 mile trip, first 40 or so mountain roads in the pouring rain no less then onto the interstate for the rest of the trip.
I suggest a 100 mile trip is nothing and better then small short trips, the key is to very the engine speed constantly as you are riding.
Someone mentioned engine breaking and I agree but gently. Engine breaking forces oil up to the heads/valvetrain. Anyway, I kind of think the trip was better for the bike MUCH better then excessive idling, being the Road King is air cooled it always had a strong stream of air running by it. My bike also has a tach and made sure I didnt exceed 3000 RPMs as suggested in the manual, cant remember if that is the exact number.
I do think, if I were you I would avoid jumping right onto the interstate maybe for the first 50 miles or so, but that is just me, then the rest of the way, take it easy, dont set any speed records and vary your speed.