How do we train for hiking 500 miles in the tropics in sand and rocks?

The terrain on the Quintana Roo coast is not all white sandy beach--in fact, I'd say that it is 60% coral, limestone and rocks, and 40% sand. It is also 108 degrees F at noon in the sun. My backpack usually weighs about 18 pounds, minus bottled water.

My father is 65 years old and I am 42 years old. To train for this adventure, during the winter months in Maine, I participate in Zumba and all other aerobics and cross country ski; all other months, I run on trails with my Siberian Husky. Also, in March, if the conditions are right, I will walk in the snow (acts like sand) on trails. By April and May, I walk with my backpack, full weight, I will even walk during my lunch break at work with my backpack. I also kayak, hike, play volleyball, tennis, bike, and surf. I have participated in a number of running 5K races, such as Komen and Race for the Cure. I was also in the US Navy for 7 years--bootcamp will get anyone in shape and start a lifetime of physical fitness!

My father has played basketball all of his life; he is on the Senior Olympics basketball team, and the number one 3 point shooter in New England for his age group. He has numerous medals. He cross country skis every weekend in the winter, and plays volleyball, tennis, bikes, surfs and hikes.

I am not exaggerating when I say that he is ALWAYS ahead of me on the coast of the Mayan Yucatan! He even carried my backpack plus his for an afternoon, because I was too hungry, thirsty, and upset that we could not find a hotel!