I will rent a double jogger for my two, 6 DS and 3DD, as my son gets sick with the heat. He NEVER uses one at home, but last summer he started having problems. We took breaks, swam, kept him in AC, gave him plenty of water, but he kept having the runs at night. ( This happened at home under the same circumstances - it is def. the heat). The days we let him use a stroller, were better. I know he may be slightly embarrased, but I think saving himself the stomach stress will be worth it to him. That said, I need to have one for my 3yo anyway, so it is not as big a decision. My point is as others have stated, do what you need to do for your family. My son is incredibly active and COULD hack the walking, but, NOT obvious to everyone else, his system cannot. Enjoy your trip!
After reading all these posts, I am bringing ours. We still have it, he still fits in it and hey, to be honest, at the end of the night, I remember wishing I had a stroller to ride in!