Are factory installed breakers already bonded

If they connect together within the mobile home, your GFI or RCD at the supply end, will keep popping as it will see it as a fault.
Neutrak and Earth come from the same point at the supply, not in the mobile home.
Consult an electrician if you have any doubts.

If they are truly grounded the bonds in the breaker box. they will not be bonded together.

For the neutral buss bar, a bonding screw goes through the buss bar into the box. Same for the ground buss bar. Usually, neutral does not meet ground until the meter, so there may only be a bonding screw for the ground buss bar. Look carefully, check with electricians.

I checked my code sheet, and only the ground bus is to be bonded to the box. The box comes with a screw that will bond the bus to the box through a bus mounting hole, the threaded hole is down there, behind the bus. The neutral does not get bonded to the box.

Problem is not clear.
You have 200 Amp cut off by meter, with 3 wires from meter box:
2 Hot wires and a ground.
http://waterheatertimer.org/See-inside-main-breaker-box.html

You have 200 amp service panel.
Does the ground wire enter service panel from cut off box?

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Any 2-pole GFI breaker typically supplies power to a dedicated balanced load, such as a pool motor or heater. Any load imbalance between either power leg (L1 or L2) and/or the neutral (N) will cause the breaker to trip on ground-fault, ie, it senses more power is going out than is coming back, so it must be leaking out somewhere and the breaker trips.
The load conductors are connected to the breaker under the brass colored screws just like a conventional breaker and the white wire pigtail from the breaker is always connected to the neutral (not bond (green)) buss bar whether the load circuit has a neutral or not. If the load circuit does have a neutral, that white neutral conductor connects to the GFI breaker under the chrome colored screw, else, this screw is left empty.
If you have any questions or hesitations, you really should have this project performed by a licensed electrician. GFCI protection is a life-safety issue and any improper installation defeats this protection.

Here's a picture of a messy amateur installation:



Look closely and find the power feeder conductors entering the panel on the bottom. The white rises up to the right and terminates in the "neutral" bus lug on the top right. The black also rises up to the right and terminates in the left "line" bus lug on the left. The red wire rises up to the left and terminates in the "line" bus lug on the right - just below the neutral lug. Finally, the ground rises left and terminates in a separate ground bar that is secured directly to the back of the upper left side of the panel box in pre-tapped holes for this purpose.

Since you are supplying this panel from your home's panel, you MUST keep the neutral and ground feeders separated in this panel (even though they will both probably originate from the neutral bar in your home's service panel). You must NOT install the long "bond" screw through the neutral bar in to the panel box. If the long bond screw is already installed, you must REMOVE it (usually this screw it shipped loose in a bag with a tag on it).

When the picture was taken, the flash reflected back making the right side of the neutral bar difficult to see - so I can't determine if the screw is installed there or not. When connecting circuits to this panel, the hot wires will of course go to the circuit breaker terminals, but the neutral and ground wires must not be mixed. The ground wires (and ONLY the ground wires) must terminate in the ground bar. The neutral wires (and ONLY the neutral wires) must terminate in the neutral bus bar. The person that wired this panel has mixed them. This would be a dangerous situation if the the long bond screw mentioned above is installed in the neutral bar to bond it to the panel box.

I hope this helps and good luck. Please rate my reply. Thanks.

Hi .. If the load center is next to the main panel you can use #2 copper or #1aught aluminum. You need to use 4 wires .. two hot, neutral, and ground. And in your load center you will need a 125amp main breaker and you will need to keep the neutral bus separate from the box, do not use the bonding screw. You will then need to install a ground bar to the back of the box for the ground wires connection.
any thoughts, questions.?

The following link explains how to correctly install a 220VAC appliance cord:

http://www.fixya.com/support/r3575913-installing_a_220_vac_appliance_cord

Match the corresponding colors at the terminal block, making sure the Neutral (White) and Ground (Green or Bare Copper) wires are NOT terminated together.

If you have any questions, please post back and let me know. I hope this helps you.