For an overnight trip just have the trailer winterized and then take a jug of water with you for flushing the toilet. For longer stays you are going to have to heat tape and insulate the water lines and add tank heaters to the tanks.
I'm in the process of getting mine ready for the winter (I'm living out of it again for work) and I have exposed lines/tanks. I've purchased 'Easy-Heat' heat tape for the water lines, added a valve to shut the water off to my outside water sprayer, stuck on tank heaters 'UltraHeat', and am getting ready to add skirting (1" foam insulation protected by chipboard around the bottom of the whole trailer). I should be good for the -20*F that was experienced last year.