I am wondering if boxing in the pipes is an option? Rerouting is a big job and ultimately, they are still exposed. I am big fan of KISS tho. And really, your pipes aren't 'full' so, a little freezing won't break anything. One of the areas to be concerned with would be where fluid collects. Low points, etc.
And one other thing to be mindful of...and it's kinda counter-intuitive, but keep a couple windows or vents open a couple inches..one at each end of the unit, if possible. We humans give off huge amounts of moisture and coupling that with the moisture created from cooking and washing, it is quite remarkable. It we don't provide a way for that moisture to escape...windows...it will accumulate in the bedding, couch, settee and clothing and you can find yourselves unable to get warm, even with the heat cranked on. And there is almost always a 'discussion' within the camping unit about it...nooo..all the heat will escape! Naw..it won't. It just means that you will be heating dry air, not wet. Try and not let a kettle stay boiling and after a shower or even a hot water wash, dry off the accumulated moisture from the ceiling and walls and mirrors. If you have a window close to the cooking area, open that a bit, while using the stove top. If you see a window getting all wet..wipe them down too. And crack that particular window open a tad..it's a gathering point. After drying the area, hang that towel, or whatever, outside if you can. Having it inside, just moves the wet from one place to another.
And..sleeping bags are not really an answer. They keep that moisture trapped. Try using actual bedding. The openness of bedding will allow the damp air out, keeping the occupants comfy. And hey..there are some pretty darned cute pj's to be found at the Cabelas store!
Fall camping is maybe one of THE best times, and you don't have to fear cold temps...just work the problem and it becomes part of the routine.
Gary Haupt