Always consider the purpose and desired behaviors of an organ when trying to determine how it will look.
Every skin material is "chosen" because it fits a role. Scales are great because they are rather impervious (which is a big deal if you are in an environment where dodging blows is difficult, or where forces like sandstorms reign supreme). Exoskeletons do this to an extreme, though they pay a price in terms of growing pains. Bare skin, on the other hand, focuses on maximum flexibility and pliability.
Generally speaking, if you look at skins of animals on Earth, gravity and air pressure have little to nothing to do with choices. The skin supports very little of the body, so the effects of gravity are minimal (other than the feet. The skin of the feet can be interesting). Air pressure has almost no effect at all until you get down into the single-digit torr range (vacuums) where the ability to create a pressure tight seal becomes useful.
As for your deconstruction system, it seems valid to me. Elephants do the same thing with mud. The only concern I might have is the health concerns of spreading processed waste (and the energy it takes to process it).
It actually strikes me as what I think of as a "falling off the bicycle" point for evolution. Realistically speaking, its much cheaper to maintain a skin compound that is emitted from the skin, rather than manually applied, especially when you think about the need for adults to spread matter on the children before they learn to do it themselves. In famine cycles, you'd have a double-whammy of no food and more damage from the outside environment. However, this sort of strange thing does seem to happen from time to time. Every now and then evolution picks something really wonky and runs with it. I recently ran across a species of bird where the males announce their stature to the females by blowing up a large inflatable red sack under their beak. The sac is nearly as large as the bird, when fully inflated, and takes 20 minutes for the male to inflate. This is totally absurd, and yet has proven to be the most effective way to pass his genes from generation to generation.
If I saw a species with such a waste-matter insulation, I would expect to see them on the bleeding edge of what their genome could do for the scenario. It clearly chose a strange solution to the problem, one which is not genetically very sound... but genetics is not proud, it simply goes for what works.
