I have found a number of trends in terms of how people have changed their mobile/manufactured homes. Most people find that they are built cheaply and need to make repairs or remodel, or people just want/need more space. (most of the homes I have been looking at are single-wide, just because it is an easy module to compare).
Porch. This is obvious, since the house is raised and almost every house I have seen has these. There are variations of open, covered, enclosed, etc:
End Extension. These are rooms or spaces added on one of the home. Variations include adding another bedroom (which poses circulation challenges), enlarging the end bedroom or living room, or adding a porch. I saw one example where a garage was added on the end.
Back Addition. These are typically enlargements or extensions of the main living space, depending on exactly where it is. These kind of slide along the back side, while maintaining a consistent front.
Siding/Exterior. In many cases where people have added additions, they have put new siding on both the old and new parts of the building, in order to give it a more consistent look, and make it not look like a ‘trailer’ anymore.
New Roof. This is one of the more interesting aspects, as people have often added pitches roofs cover their homes. Sometimes this is because the old roof leaks. In other cases, it helps tie new parts of the house together, creating sheltered exterior spaces and gives a new, and sometimes dynamic form to the house.
Remodeling. Because of the quality of the materials in a mobile/manufactured home (2x2 or 2x4 structure) wall paneling, and other cheap finishes, many people decide to remodel their homes once they get a little more money.
When all these small incremental changes are added to the original home, it is often difficult to tell whether it ever was a mobile or manufactured home.