Three Weeks Until Trip

Three weeks until our trip to our home state to see family, including my stepkids.  Stepkids sounds a little funny now that they are teenagers - stepteens?

I need to find more room in our vehicle for our road trip.  With six people and luggage, it's a tight fit so I am looking for either a cargo bag or some type of device to put our luggage somewhere other than in my car.  I have a hitch for motorhome towing so I thought I'd either get a waterproof bag for the top rack of my truck or something that can use the trailer hitch that carries cargo. That way, we can bring our guitars on our vacation and keep those in the truck with us.  Otherwise, we are all packed into our vehicle like sardines with our luggage. 

My daughter wants to bring her guitar and I want to bring mine too.  They won't fit in the car unless we can find a cargo carrier to put our clothes and toiletries in.