I asked before about freezing water pipes, but got no replies. My water pipes are on the inside of my home, not underneath. So why does the HOT WATER freeze all the time and not the COLD when the pipes are inside the home? Also how does the main drain freeze and end up in the bathtub?

Amost always, you water mains run in between the floor joists and vapor barrier under your home only the risers from these mains run inside the walls. I would be looking for any breaks in the vapor barrier. Especially near the exterior walls and crawl space vents. Cold is one thing, add air movement of any kind and the problem triples. Also suspect are any risers in exterior walls, including your water htr space or location...most are near exterior walls. Hot water pipes have cold water in them until you use something, at night there is plenty of time for freezing hot lines. You are looking for a section of hot line directly exposed to air movement or a line in a exterior wall that has no insulation between the pipe and the surface of the outside wall. One more thing, it is very likely the cold inlet line going to your water htr if all of your hot water is affected. The cold feed for the water/htr often branches off the cold main near the bottom or under the water htr. This branch often is exposed to cold crawl space air near the water htr. If you have a double wide, the "jumpers" used to tie the hot and cold lines into the other half of the home upon setting the home are often done exposed and carelessly...a reflection of the home installer not the home manufact. These jumpers are usually the only exposed lines below the vapor barrior, besides your incoming cold water service. Real bad freeze...leave your sink cabinets open at night and let your hot water slightly drip through a faucet until you can insulate the offending section of pipe. There. that just about does it. Age of home and # of bathrooms would norrow it down quite a bit.

Camp,
Many folkd did answer your questions about the freezing issues you have with the pipes. Refer back to them.
Insulation on pipes will help prevent them from freezing, but the biggest reason for a pipe to freeze, regardless of hot or cold is wind.
If the pipe that is freezing is anywhere there is an opening that can either catch the wind, or allows a breeze to blow by the pipe will surly freeze. Wind will take the warmth out of insulation in a very short while.
So where ever this pipe is located you must stop the air from entering, then make sure the insulation is packed thickly around the pipe and if at all possible because its a mobile home, heat tape any exposed pipes that may be exposed in the area of the hot water heater.

In any case refer back to the past responses as many folks had other ideas on why this happens.