Sorry York, I had to chuckle when I pictured folks wearing PFDs in their driveway! Reminds me of a joke I won't repeat here!
I rigged my boat all the time in the driveway to make sure every thing is ok before towing to the lake. If you have transom straps or other straps securing the boat to the trailer, and keep all your sheets free, it would really take alot to topple the rig.
One thing to watch for, is depending on how heavy you are , and how the boat is supported on bunks on the trailer, you could potentially damage the hull by placing too much weight on just a few pressure points (rollers or bunks) that were really designed to hold the weight of the boat, and not much more. I try to avoid climbing into my boat when its on the trailer....fortunately, I have lightweight kids who are much better suited to scrubbing the deck than I am! ;-)