You REALLY, REALLY, REALLY need an attorney to assist with preparing a defense in this case. It doesn't sound like your brother's claims of non-payment fraud, etc. are very strong, but you need a local attorney to draft an Answer for you within the 21 day period. If you try to do this yourself, you could potentially hurt your case, as your Answer will need to assert a number of particular and highly nuanced affirmative defenses, all of which must be raised in your Answer.
From my perspective as a Bankruptcy practitioner, assuming you hire an attorney to handle the state court lawsuit, an even bigger problem could be a preferential and/or fraudulent transfer action by the Trustee in your brother's bankruptcy case.
Your brother purchased/financed the trailer in November 2007 with only your name on the title. Your brother then filed bankruptcy in August 2008 (without disclosing the trailer in his Schedules), less than one year from the date he purchased the trailer and (arguably) transferred the title over to you. However, the secured LOAN was in your brother's name, so the LOAN should have been disclosed in the bankruptcy (which likely wasn't done, or you would have likely been dragged into your brother's bankruptcy proceeding back in 2009 - you might have won on the merits, but this issue certainly would have come up and been litigated had your brother disclosed everything he was supposed to at the time he filed).
Under Section 547(b)(4)(B) of the Bankruptcy Code, a "transfer to an insider between ninety days and one year before the date of the filing of the petition" may be considered a preferential transfer, and the Bankruptcy Trustee can "clawback" (i.e. take) the property from you, even if your legal title to the property is completely legitimate under state law and you own the trailer free and clear of all liens. A fraudulent transfer under Section 548 is similar, except it allows the Trustee to "clawback" property transferred within TWO years of the date the bankruptcy was filed.
You need to be aware of this Bankruptcy issue, as the Trustee will likely come after you to recover the trailer if you win in state court. You should discuss all of this with your attorney and plan accordingly.