Form 5498-SA is an informational form (for you) and it does not need to be reported on your tax return.
As for the 1098-C, the IRS says "A donee organization must file a separate Form 1098-C with the IRS for each contribution of a qualified vehicle that has a claimed value of more than $500. " This means that the IRS gets a copy of each form, so you should report each form (if you get one).
The FMV value determination is up to you; in case, of an audit, though, the IRS will ask you to justify the FMV you arrived at. For household items like furniture and clothing, you can find valuation guides at the Salvation Army and Goodwill websites, but I doubt you will find values for boat trailers. Contact a dealer of used boating equipment and see if they can help.
As for your last question, it depends on whether you are asking about federal or state taxes, and which state. Please post a new question given more details.
