I will put in my 2 cents having lived in my trailer in winter in many states. Two words- Double Up! Heat tape that is. If you don't have a ducted furnace you will be using heat tape to keep pipes from freezing yes? If one of your pipes freezes do you really want to rip the bottom open, crawling around on the frozen ground trouble shooting heat tape? Nah. Unplug #1 and plug in #2.Maybe problem solved. A little more initial expense but you saved all that money buying a 3 season trailer! Insulate any water lines after heat taping, I have used the cheap foam stuff in winter( with heat tape) never a freeze up on my supply line. I used to use copper in winter but changed to PEX with great results. You may want to put heat blankets on tanks(they make some nice ones for engine blocks) if you are planning to keep bottom unducted.
