This is a very lengthy process that requires a license, experience and the correct tools in order to get the job done correctly and safely. People ask me all of the time how we get the two pieces of a mobile home together. Since double wide mobile homes are delivered on wheels and axles and arrive in two different pieces, it is understandable the the setup process can be confusing to someone who has never seen it happen. Hopefully I can help answer some, if not all, of your questions regarding this matter. I will do my best at explaining but it will be lengthy because how many different factors are involved.
Here is how it works. Generally people know exactly where they want their home before they buy it. That being said, the home is delivered to the location one half at a time. Depending on the location and the pad that the home will be set up on, either the front half (AKA The A Half) or the back half (AKA The B half) will be spotted exactly where it will be set up. The other half will be pulled beside it at a distance of 2 to 3 feet from the other half and as parallel as possible. It will also need to be lined up from end to end as parallel as possible as well. The next step is to remove the plastic that covers both halves and make sure that there are no nails, staples or anything else that might keep the home from fitting together tight at the marriage line. After this is done then the half that is already exactly where it needs to be is setup on blocks and leveled with a water level (which I will talk about in a different article) NOT A 4 FOOT LEVEL. Generally, the axles and tires are removed from that half of the home at this time before proceeding to the next step. After this is done then the unset half can be rolled to the setup half. On a side note... generally all new homes being set up there will have plastic put down on the ground under the entire home and under all of the piers. This is a vapor barrier that keeps moisture from coming up into the home and is required on ALL new homes that have skirting put on them.
The are are a few ways to roll a home together. The traditional way is to use bottle jacks and a roller system. A newer way is to use a Cutting Systems "Platypus". It is basically a mini machine with Bulldozer style tracks that has a long hydraulic arm on it. It is pulled in from the side of the home and by the push of a button it will pick the entire half of a home up. At that point you simply drive it straight forward to shove that half over to the other half. Click Here to see a video of someone using this type of system. The first way that I mentioned, "the roller system", consists of aluminum or steel channels that are 4' or longer in length, a roller tray that fits down in the channel, and a top plate that sits over top of the roller tray (the top plate is what the bottle jack sits on). The roller tray is a small piece of aluminum or steel channel that has 5 to 8 rollers built on to it that roll on bearings. Once the complete system is set up and the jacks are on top, the jack is jacked up to the bottom of the I-Beam frame of the home. After the home tires are not touching the ground anymore, the home will simply roll sideways by putting a come-a-long from the I-Beam of the set half to the I-Beam of the half that is on jacks and rollers and pulling it together. Most generally, it will take several sets of roller systems to complete this. A general rule of thumb is to place one tray in front of the axles and one behind the axles on each I- Beam (There are 2 I-Beams on each half of a Double wide). In addition to these four systems, there has to be one under the tongue of that half so that the entire half can roll all at once. Here is a link to a company that sells these systems. There are diagrams on this page that show how these systems look when getting a home ready to roll. http://www.perfectaline.com/Multidirectionalsystems.htm
Usually what happens next is the two pieces are put together as tight as possible and the floor level from one half to the next is lined up as close as possible using the jacks. Lag screws are then put in from under the home from one half to the other through the marriage beam joist. Lag screws are what hold the bottom of the home together. The water level will be used again at this point. While the rolled half is still jacked up in the air, blocks are brought in, and then piers are built to be level with the piers of the half that has already been setup. At this point, the second half can be lowered on to the piers. 99.9 percent of the time after this is completed, if you look at either end of the home on the marriage line up top where the fascia comes together, the two halves will not be squared up (lined up) and there will be a gap between the two halves. This is fixed by "racking" a home. By jacking on the outside I-Beam of one half and on the outside I-Beam of the other half on opposite ends of the home, it will squeeze the tops together and line them up as well. The home is then lagged or bolted (depending on the brand of home) together at the top. Next, the flashing and/or tar paper, center roof vents (if applicable) and then the shingles are put on last. The racking jacks are not let down until after the top is lagged and the flashing is put on. The inside and outside walls are then screwed or bolted together and the main part of the setup is done. Now, in order to finish the home, there are a lot of little things that still have to be completed at this point. The main things left to complete are hooking up the water, electric, and A/C crossovers, anchoring the home down, installing door and window piers, and removing the axles and tongue. From this point, a trim-out crew will usually come in the following day and finish the trim on the inside and outside of the home where the two halves come together. In a nutshell... that's about it!