questions.... I have them.. :D

You fill you tank probably theough the same hose for the winterizing thats attached to your pump. You could elongate that line to the outside or underside and use it that way also. As was said you can get a separate pump and fill from a bucket also. Changing out to a gravity feed can be done, but you have to have acess to the water tank and make some holes in the camper to do it. Probably not worth it. Easier to drill a hole in the bottem of the camper and extend the winterizing line. ( just check that yours fills the tank that way, check the owners manual)
I would use antifreeze myself, i dont know how you can blow out the water in the water pump on a camper. If it doesn't get that cold during the winter it may not matter. The choice and chance is yours to make.