We did when we had the solar panels + inverter + new batteries installed a few years ago. Being fulltimers, the RV is our primary residence. At that time, the credit would also apply to "secondary residences" such as vacation homes or RVs. In our case, it was the cost of the inverter and four deep-cycle gel cells that drove the cost up to the point where the credit was worth filing for.
We use TurboTax, and there's a specific set of questions/forms that are used to enter the info. We'd planned the inverter and new batteries, but adding the solar made all that into a "system", and made it all eligible for the credit. The credit ended up being just about equal to the extra cost of adding solar to the other stuff. We had it all professionally installed, and so the amounts we used covered parts and labor. If I recall, the limit on the credit back then was $2000. I think it might be higher now. Don't remember what the credit percentage of total cost was - something around 20%.
That was for the Federal taxes - if you file state taxes (we don't), there might be additional opportunities.
al
