Re: Purchased used trailer w/ no title
If MD has different tax rates for boat, motor and trailer; learn what those rates are before you start the process. There might even be a grandfather clause that exempts paperwork for trailers over a certain age.
Another option is to find a close-by state that doesn't require boat trailers to be tagged and claim that it came from one of those states (if the time and paperwork factor make this option viable.) In the case of a small-value item, the overriding interest for the DMV is to establish a revenue stream. Tell the clerk a believable story and it'll probably pass muster.