My Springdale TT started getting cracks in the original factory supplied tires after 3 years. I was a little concerned, but decided to wait. In the 4th year, the cracks didn't appear to grow, but didn't go away either. 5th year, I decided to change them. I never had problems simply because they began to form little cracks. I think if you use your camper, keep it rolling on the road, it will keep the remaining rubber pliable and slow down the cracking. Rubber needs to be flexed and used.
However, no one can make the decision for you. I will suggest though, if it troubles you, or you have any questions or doubts, then follow your gut instincts and get new tires. Worry on the road with the original tires can absolutely rob your joy and fun on your trip. So, if it will gnaw away at you, go ahead and change them, and travel with peace of mind.