I guess a finer cut on the definition of "boondocking" is in order!
My definition of boondocking not only is "drycamping out in the middle of nowhere in good comfort", it also includes "drycamping out in the middle of nowhere in good comfort in places a bit tricky to get to".
This definition implies a small, compact RV - which makes it a bit tough type of camping to get to in too large, or too long, of an RV. The "in good comfort" and "in places a bit tricky to get to" parts of the definition also mean a suitable RV for the OP can wind up being a bit cramped with a family, but finding an RV to meet this definition's tight conditions is possible - although they will be few and far between whether looking for new, or used.
With my definition and the OP's family situation, and wanting to expore beyond a base camp, a small fith wheel would be about the only way to boondock and still maintain complete comfort. Towing a fifth wheel is superior to towing a trailer because a fifth wheel places the tow point and a lot of it's forward weight over, and slightly ahead of, the rear wheels of the tow vehicle for superior tracking and stability. Tow vehicle road surface traction is also superior pulling a fifth wheel because much more weight is not only on the tow vehicle's rear drive wheels, but more of the of fifth wheel's weight is also transferred onto the tow vehicle's front drive wheels (assuming a 4X4 tow vehicle). Of course with a family, the tow vehicle would have to be a 4X4 crew cab bodied pickup truck.
Here's one of the hard-to-find examples of a small fifth wheel that might come close to meeting all of the OP's requirements - if they want to boondock in places a bit tricky to get to:
http://www.roamingtimes.com/rvreports/1/scamp-fifth-wheel.aspx