I have inspected damage and/or estimated remodels on literally thousands of mobile homes as a repairman. What Greg said is absolutely true. I see many homes from the 70's that are in excellent condition and homes at 10 years old or less that are trashed and even structurally compromised.
I would say by far the main culprit to damage is water, whether it is a roof or plumbing leak. These areas should be your primary focus when maintaining your home. You should inspect your roof from the top side and take action before a leak situation occurs. Waiting to see spots in the ceiling allows too much damage to happen.
On a somewhat newer shingle roof, you would be looking for obvious recent damage such as broken or missing shingles and dried out sealants near vents and protrusions. You also want to keep an eye out for your installers work quality, such as shingles not stuck down at the edges, bumps from nails or staples lifting under shingles and areas that may looked "forced" together.
On shingle roofs 10 years old or older, look for curling of the shingle edges, especially at the bottom 2-3 courses and inspect the side edges of the individual shingles. If you see wear, as in missing mineral coating or worse yet, exposed fabric scrim, you are very close to needing a new roof. 20 Year shingles rarely last 20 years without leaks. In my area where it is very hot in the summer and exposed to a lot of sunshine in all seasons, 20 year roofs are good for about 12 years usually. There are maintenance things you can do to prevent leaks, but not a lot you can do about aging of the shingles.
On metal and coated roofs, you are looking for the earliest signs of cracking. Just because you see a small crack in the sealants does not mean that spot is leaking. Often times the sealant near the crack is still holding up. But cracks can limit the effectiveness of the subsequent repair and maintenance. All sealant areas should be fairly smooth. I have seen many roofs where there is a build-up of old sealants that were just painted over old damage, creating rough, gnarly looking areas. New sealants wear out quickly on rough, sharp points. As metal roofs get older, the metal often relaxes to the point where it will create small dams near the eave edges, causing water to pond. Even small ponding areas can cause problems near the edge as they continuously feed small seeping leaks for longer periods of time. Short of installing a new roof, there is usually not a lot you can do to remove these ponds. Your best defense here is to upgrade the types of sealants. Typical acrylic elastomeric sealants found in home stores do not do well in ponding situations. There are sealants like Ame's Research Elasto-Barrier and a product called Liquid Roof (EPDM) that are proven to work in ponding situations.
Probably the second biggest source of damage I see is termites. Termite damage is almost linked to the above water damage as the termites will always have a source of water. Leaking pipes from the home or sprinkler system are main causes. You can also have natural causes providing this water. Denying termites a water source and removing all non-treated wood and brush debris from the ground around the home is the first step. Regular inspections looking for mud tunnels, especially on concrete blocks and backs of wood skirting, and areas of damaged paint, showing bubbling, wrinkling or separation, helps keep the bug problem from getting out of control. DIY efforts should mostly be on the prevention side of pest control. Once a home is infested, you really should call a pro. There are liquid treatments to repel or kill termites and the detection spikes are excellent as they will show you where the termites are coming in at are common measures. Also the use of a certain sized sand is very effective without being toxic to anything. Sand that just barely passes through #16 mesh screen (an not smaller) is excellent. Termites cannot burrow through this size. they cannot displace it with their mouths and cannot burrow around it. Lot's of good information online about termites.
Hope this helps.
Today is PERFECT!
All information and advice given is for entertainment and informational purposes only. The person doing the work is solely responsible to insure that their work complies with their local building code and OSHA safety regulations.