I don’t have any advice or insight in regards to the altitude change; however, I’ve traveled with buns quite a bit.
Get yourself a small pet carrier–you don’t want it to be too big; the less area for your bun to roll around in in case of fast starts and stops the better. Plus your bun will likely be scared and not move much during the trip. I always put an old towel down in the carrier; it never fails that Pumpkin ends up peeing during the trip (even if its 20 minutes to the vet!). Two hours is pretty short, so you shouldn’t need to stop for stretch breaks. Don’t panic if your bun doesn’t eat or drink during the trip, but offer up lots of hay, water, and we veggies when you get to your destination. Neither of my buns will eat on car rides, but my first bun Boston would munch hay and veggies.
You might want to put your carrier on the floor if you can as that the safest place, but you don’t want a vent blowing into the carrier. When all else fails, I talk and sing to my buns. In my head it makes them feel better! 