They're getting to the age when camping with the folks is out of their radar. :)
One idea would be for you to set the limit of miles from your home for your trip. Also, you'll probably need to set a daily allowance of how much the family can spend!
Then let them jointly or individually plan the whole trip. They can do research on the net for places to visit along the way or when they get there. They can research prices for attractions. Give them an amount on how much you're willing to pay for a campsite. This would be a good learning experience for them on how to budget money. Kids don't have a clue how much things cost.
You might have some interesting trips!