We will be driving 9 hours next week to the. Mountains and I want to take the new to me subaru rather than my wife's pilot with 210,000 miles on it already. I already have a Thule box to put on top but with the wife two kids and my 100 lb Chesapeake bay retriever space gets eaten up quick. Dog will go in way back and I am planning to put a hitch with a platform on the back to put the cooler and a largish Rubbermaid bin on. Is anyone else using both a cargo box and and cargo platform on the back. Should I be concerned about overloading the car by doing this? Thanks for the help.