... Can I claim the wiring work I've done this year or can you only deduct the panels and controller themselves?
Let me start by saying that you are asking here for tax advice, which most people are going to be reluctant to give, myself included. So with that in mind, I am going to say that I am not a tax professional, nor do I play one on TV (or the Internet). My opinion is just that, an opinion, and should not be relied upon to carry you through an audit. Lastly, even respected professional opinions can be useless against a grumpy IRS auditor who has elected to pursue this item on your tax return.
All that said: The 30% federal credit for photovoltaic systems may only be taken in the year the system is brought on line. So, no, you can't take the deduction until you actually install the panels, controller, and anything else you need and the system starts producing electricity. The wiring specific to the photovoltaic system is an allowable cost that can be deducted, so save your wiring receipts so that you can include those costs next year or whenever you finish the system.
I could be wrong on this but I think tax credits can only be if it is installed on a house not a motorhome conversion.
This is a gray area. The code says "residence" in the US. For certain energy credits, it must be your principal residence, but for solar energy it can be any residence.
If you are audited, the auditor may challenge your motorhome as a "residence" -- but note that the code allows you to deduct the mortgage interest on your motorhome if it is either your principal residence or your lone secondary residence, and this is commonly done throughout the industry.
If you use your coach only for weekend trips on an occasional basis, you might lose the residence case, especially if you already have multiple residences. But if you live in your coach full or part time, you are probably OK.
We live in our coach full time and took the credit back when we installed our panels and controller. Our tax professional agreed with it and we did not get flagged for audit. We have since been audited for other reasons and this did not come up.