What you want to do with the ground at the Siemens load center (if I understand things properly) is fine. At the main disconnect the ground and neutral are bonded together and once that is done you can use the lugs, busbars interchangeably.

I'm more concerned with the feeder being connected to the lugs. You need overcurrent protection on that. Note that you will now run four wires (your two hot legs, the neutral and the ground) to the new structure (mobile home). You will also need a grounding system at the new structure.

"I'm more concerned with the feeder being connected to the lugs. You need overcurrent protection on that. Note that you will now run four wires (your two hot legs, the neutral and the ground) to the new structure (mobile home). You will also need a grounding system at the new structure."

By "feeder" do you mean the load side coming from the meter to the load center/disconnect or the load side of the load center/disconnect going to the mobile home? There is a 200A breaker in the load center to act as a disconnect and of course another 200A main breaker inside the MH's breaker box. And yes, I assumed another ground would be needed there, but the men who move the MH are connecting that end. I've been out pricing 4/0-4/0-2/0-#2 AL at Lowe's for about $3.70/ft.

Another question, if I may. There is no distinction between either of the "hot" legs traveling from the meter through the disconnect to the main breaker in the home or are they kept left and right, so to speak, all the way throughout? Keeping them identified from the meter to the disconnect is obviously not a problem but from the disconnect to the home at least 100' away would require identifying them before being buried.

Yes, that's what I meant by feeder. From the mention of "feed through lugs" I thought you were feeding the motor home panel from the main without a breaker.

There's no phase identity. As long as you don't connect them together you'll be OK :-)

Thanks. No, everything coming "through" that load center, including the through feed lugs at the bottom, first passes through the 200A main breaker at the top. I should be good to go.

Now again you're confusing me. The "breaker at the top" isn't the issue.
Is the feeder to the MH protected by it's own breaker or not?

The feeder is protected by the main 200 amp breaker within the panel. The service entrance goes to the 200 amp breaker first then out through the feed through lugs. The feed to the shed does need an additional breaker since it is less than 200 amps, therefore a 100 amp breaker is installed in one of the few extra breaker spaces.

That's exactly what I'm planning to feed the shop/barn.

So far, so good everybody. The PoCo energized us yesterday and said everything looked good. Haven't connected a load to the load center yet.

I have OCD. Keep left left and right right. It's not hard. Before hooking the cable up, connect one hot to ground, then go to the other end and identify it with a continuity tester.

Of course it's too late now. :P

You'll never find any of my work where they're not consistent, nor will you find a two-pole breaker that starts on an even row.