I live in a small mobile home in Palm Springs. The trailer itself is somehow attached to a nice add on. I suspect that the trailer part of this home needs to be inspected underneath since I think it may need re-levelling, or whatever it is they call it. I have had no experience with any of this. I asked my neighbors since many of them live in these types of units and no one seems to know how to go about it. Even if I go under the trailer part myself I have no idea what to be looking for. I know the tires to this thing are still there, but it is not resting on the tires, but on some things that appear to have been placed there for the sole purpose of having this unit on it, and perhaps as the years have gone by, they need some work. I can see what the unit is on and I believe it is wood. Has anyone out there dealt with this>

Which is higher, the trailer or the addition?

You should call a local mobile home dealer and ask them who they would recommend to properly level out your home. It is more complicated that you can imagine and no, you cannot do it yourself as you do not have their expensive leveling tools or equipment. You may also need additional tie downs as well. I have seen them level out single wides and double wides. It does not take very long either.