Given you have a 30 foot box truck, that makes things a bit difficult getting around parking areas. I would suggest Parking at NCAR Mesa in Boulder. There is a lot of parking and you can find a spot that you can take up as many parking spaces as you need. Access is easy to get in and out of the parking area. There are many choices of hikes you can do from there. Mallory cave is only about 1 mile in and is a beautiful hike. Bear Canyon is a fairly easy hike and you can turn around at any point you feel like it. Fern Canyon to the top of Bear Peak is strenuous. There is also the Mesa Trail which takes you in either direction along the base of the Boulder Mountains. If you don't bag any peak, it's still a great spot to go, providing your allowed to take your truck that far.
Here is a more detailed page for the area with directions to NCAR Mesa. http://www.summitpost.org/boulder-group/153333