Travel by car in third trimester

So I mentioned to my midwife the other day that we are leaving on vacation mid July for two weeks and she was not for it. We’re driving for about five hours to meet with friends in the mountains though I won’t be doing any hiking. It’s a rockclimbing trip so I’ll be sitting at the cliffside in a portable chair my husband bought me. He picked out cliffs with very short walks to get to them (like 2 minutes). So I feel she’s overreacting—I’ll be 32 weeks when we go. Last pregnancy we flew to South Africa at 5-6 months and my OB was fine with it. But does anyone have any advice or experience with longer car rides during the third trimester?