DebnAl,
When I spoke with Ron at the hitch shop, he assured me that adding a receiver for a bicycle rack would not impact the frame warranty. If a receiver hitch was for towing a small trailer, or building a rack for a motorcycle, would potentially void the frame warranty. The Bicycle rack w/ 2 bicycles is only going to weigh about 100# at most. I explained to him how the rear cap of the BC comes out to a point at the center, and he said that would not be a problem. The actual receiver end can be made to just about any length and ensure proper clearance for the bikes while on the rack.
As far as the Caster Wheels, Ron would first install the receiver hitch, then he would build a custom bracket to ensure that the casters will be 1"-2" below the receiver hitch. This would ensure proper clearance when we back the BC into the driveway and storage. Ron is a real perfectionist, and he really knows his stuff. The Caster Wheels have a 12,000# capacity, and are about 5" diameter, and swivel. I think his price quote seems pretty reasonable, especially considering everything is custom fab'd to our BC.