Lots of issues here. If I imagine running into this situation in my local area, these are the issues I would probably encounter. OTOH, you might have the same, or totally different issues completing this work.
First, the service wire from the panel to the meter and the meter to the utility connection point is not large enough to support a 100 service. Second when you upgrade that wire you will need a new meter base that is approved by the utility for their meter. If he service is on a stand alone pole that is part of the "customer side" of the service, it may, or may not suit current codes. I've seen poles that are too short to allow the utility to install their wire at a safe height and multiple poles that rotted and fell over. Next you will have to install additional grounding at the service, including two ground rods, and the proper ground wire. Next the installation needs to be inspected by a licensed inspector who will issue a "cut-in" card which will allow the utility to connect the power. This inspector will want to do a general inspection of the homes system to look for aluminum Romex, grounded outlets, GFCI protection in kitchen and baths. As a result, a significant amount of upgrading to the electrical system inside the trailer may be required.
Not to be the bearer of bad news, but these jobs, in many heavily inspected areas, can turn into a real cluster F. In other areas, they can be cheap and easy, if there is no real need to get inspectors involved. My local utility requires that everything get inspected before they reconnect, so there is no way to work around the issue. Good luck.
