Since the ceiling, wall and floor cavities for many manufactured homes are sealed, it is difficult to add insulation. However, some models have attic spaces in which you can install extra insulation and some insulation companies can blow insulation into the floor cavity.
In new homes, look for a minimum R-value of R-11 for walls, R-19 for floors, and R-30 for ceilings.
Make sure insulation has not shifted during transit before joining multi-section homes.
See that the “marriage walls” are airtight with foam gaskets installed between sections.
Seal all plumbing and wiring penetrations using expanding foam or caulk.