What are some things that might make it fun for him?

Check out the book on Carschooling from the library (there's a review of it somewhere on this site). It has lots of great roadtrip ideas that are both fun and educational.

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http://stuffedveggies.blogspot.com/

A road map of where you are going. He can follow along and point out the next town, city, etc.
Snacks! Boys love to eat, lol!
If you are ok with cards, show him how to play Solitaire and a few other "one person" card games.
Play I-spy with him. Use 30 minute dvd's occassionaly to help break up a long drive. (This will require a portable dvd player if you have one, if not, then forget it, lol)
BOOKS.... plenty of books and magazines. Ranger Rick, HIghlights, etc.

Books, magazines, snacks. I used to love just looking at the scenery and you guys should have plenty of scenery. We used to have little tv's that attached to the back of the head rests and our kids watched movies on long road trips. They were not very expensive and gave us lots of peace and quiet.

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Mom to Christian (13), Saphira (10), Xavier (5), and Adrian (2).

When my daughter was little I strung a piece of string or elastic across the front of the car. On the string I put old spools. When we would pass 10 miles, I'd slide a spool across to the other side. That gave her a good visual reference of "are we there yet?"

License plate watching. When we went on our long trip a few weeks back, we kept count to see how many different states we could see. We kept a log for each day in different colored pencils so each day we counted the first plate from each state (other wise you could have 50 of WI, 10 IA... so each state got one count)per day. We did keep track of how many Canadian plates we saw each day and which province as well.

We also played a bingo game we had found. You could create your own. Ours had two choices, town or country. You'd be looking for a cow, or a mailbox, a horse, a school bus, a windmill, a convertible, an airplane, a car with 1 person in it, a car with 3, a house, a tractor... for country. For town it would be a post office mail box, a plane, a train, a shopping cart, pedestrian crossing, school crossing... You could decide what you wanted, draw an rought sketch or a word, or a sticker into each box like on a regular bingo game. Squirrels were very difficult to see when driving so, might not want them.. kind of thing, but you could put a deer, whatever animal might seen in your area.

That whiled away many hours and we had so much fun doing it.

One made up game my dc and I used to do when they were small was "Build a Car". A blank piece of paper will work and basic drawing skills.
We'd have to build a car from the pieces found on the side of the road. You can make it as elaborate or as simple as you want. Four tires (even shredded ones count, lol), 2 bumpers, etc.
Each time you see a piece of a car, you draw it on your paper and whoever gets enough pieces to make an entire car wins. (For entire cars that are broken down, each player gets to pick one piece of the car.) The first person to spot the piece gets to claim it.

Yes. To me, it would. For example, nobody's "pushing" for three wise men and yet it is important for me to see/know that it does NOT say that there are three wise men.