I'm interested in the replies for a similar, maybe more common situation.  I live in a nice, new "spec" house (built on the speculation that someone would buy it).  I'm stuck with the design flaws and can't really complain too much given the circumstances.

My issue here is a severe ineffiency (in the energy sense) that is very common in modern homes. Before they pour the concrete slab, they stub in all the plumbing with no insulation of any kind. True to the standard, cookie cutter design, the hot water heater is in the garage; from there, the hot water goes right into the 'crete where it cools nicely. I can accept having to let the hot water faucet run for a bit before I get hot H20, but it seems to take no more than 2 to 4 minutes without running for it to cool back down to slab temperature.  It is a shining example for utilizing geothermal energy, but in a perverse reverse.

Why don't you run a POU On-demand hot water for your needs? Here's a place that I found cheap ones. I bought a low flow shower head from them and they were nice people.

As far as running under ground, it's a hard one, I want to run a line from a spring on my property that's about 100 feet from the house and I don't want to dig the 4 foot trench required to keep it from freezing. The only way to do it is keep the water running and I don't want to do that so call the back hoe!

I thought about running the water line from a heating source under ground to the trailer house also. My thought was to slice open a larger piece of pvc (2" or 3" ?)
Cover the 2 halves with something (Kitchen wrap?) so expaning foam won't stick to them. Then space the water pipe as I want it with a few pieces of foam for support.
Clamp 2 halves of external pipe together and fill with expanding foam. Once cured remove external pipe and I'd have a nicely insulated water pipe I can slide inside a solid external pipe the same size as my mold pipe was.

I figure cutting the mold pipe will make it slightly smaller diameter (blade thickness) and that should let the finished insulated pipe slide easily into a permanent pipe.

Also using half pipes for a mold it should be easy enough to be certain the inner pipe isn't drooping to the bottom anywhere and is evenly centerd before filling with expanding foam.

I think I could drill one half with holes every so far for filling the mold so I have no empty voids, easy shave off any fill sprues left and when slid into the permanent pipe there would be no holes to worry about except joints and ends.

Could leave ends of inner pipe exposed to permit easy connections, slice external pipe or couplers in half and glue together and fill with foam after installing pipes easily if using pvc type pipe for external.

Several other reasons I thought this might work well, like if a pipe gets broke it's easy to replace, making specail sizes or joints etc..
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nothing to lose

5. yrs ago I did an 80' well-line in N. Minnesota...about as cold as it gets, shy of Alaska anyway... <g>
1. " black-poly tubing, and I used the thickwall version even tho it's harder to handle.  Better insulation, and far more resistant to crushing from rocks intruding where they don't belong...

The cabin was about 20' back from the edge of a sandstone bluff over a river, so there wasn't a lot of overburden.

I dug the trench with a backhoe, down to bedrock the whole way.  Soil at the cabin wall was only 30" deep, tapering down to about 7' deep at the wellhead.

The entire tubing/heat-tape/insulation assembly was laid in the trench, and then we slid 10' lengths of thinwall 4" PVC over it.  This pipe is made with one end formed larger as a female, so no couplers are needed.

I did NOT glue the joints, as that almost guarantees that it will eventually fill with water.

If you're doing this right, you will have designed the trench for proper drainage.  We put a thick layer of clean coarse sand on the bedrock the whole length of the trench...a foot thick at the cabin...increasing to maybe 18" at the well; then laid the line on top of that.

After the PVC was installed, and all hookups were made, we laid another 6" of sand to fill the trench to just over the top of the pipe.  Then we cut 4x8 sheets of 2" pink-styro insulation into trench-wide strips, again running the entire length.  Another 12" of sand over that, followed by pit-run to fill to top.  Be damn sure you don't have any rocks near the line, because they WILL move during freeze/thaw, and eventually pinch off your line.

Temps at this location were in the -30 F range for a few days at a time several times each winter.  We'd usually turn on the heat-tape when it got down near zero, but forgot once or twice.  Never had a problem with this.

You might think about what else you'd want run too...