I am a physical therapist and treat patients with total hips all the time. Based on your original post it sounds like your DH is young and healthy except for his hip. What he can and can not do depends on the type of surgery (surgical approach), type of implant and what restrictions the surgeon might place on him. The surgical approach will determine what precautioons he must observe after surgery. The type of implant and cemented vs. non cemented will determine how much weight he can bear and how soon.
My biggest concern would be blood clots (DVT) especially if you are flying. Blood clots in the legs can occur after surgery especially orthopedic surgery and can be common when people fly (even if they haven't had surgery).
If you are driving then stopping every 2 hours is essential to allow him to walk around. Sitting in a car with the seat pushed all the way back is better than being cramped. Doing ankle pumps (pulling your toes up and down at the ankle) is something that can help avoid this. As for the walking take it easy. I have had patients back to work in less than 2 weeks, commuting byt ttrain and subway! Of course they are younger patients in good physical shape except for the hip.
Ask the surgeon and the physical therapist and see how he does after the surgery. If you decide to rent an
ECV then make certain that he can extend the surgical leg forward as he rides and get off it and walk around, sit a in a chair etc.
Again depending on his type of surgery if the doctor says avoid hip flexion (bending over 90 degrees) avoid things like Space Mtn, Rockin' Roller Coaster becasue fo the extreme sitting position and Tower of Terror because of the jolting.
Good luck with the surgery and have a great trip!!!