I bought a five year Maine tag for my boat trailer 3 years ago. Google the Stabb agency they will handle all the paperwork for $25, you fax them a limited power of attorney and the walk the paperwork through for you, tags come in the mail in a week or so. Very simple and far cheaper, my only regret was not getting the 10 year tag. FYI Maine does not give titles for trailers, your bill of sale is your title. Also as I understand it from 2013 it is legal to register in Maine if you have another trailer registered in Maryland. No one ever checked on this then or since, I have a small utility trailer registered in Maryland.
I just did this, through National Trailer Registration, 10 year tag, total was $220. Just had to send them limited power of attorney, bill of sale, proof of taxes paid to Maryland DMV and a copy of my Maryland title. Very easy transaction, just took a couple of weeks.
I went through National Trailer Registration and it was a piece of cake. I have travelled from baltimore to OC muliple times with zero problems. I highly recommend my on regret is also not doing for 10 years
The process is painless, just fill out the form, provide proof of ownership and send a few bucks. LEOs in my area were harassing me so I went legal a few years ago. When I had mine a few years ago the fine was $1500 if you didn't have at least one trailer registered in MD, and I had recently gotten ride of my MD registered motorcycle trailer. I don't know of recent enforcement but the LEOs for a while were scouting boat ramps - revenue.
If you live in Virginia, the permanent trailer registration fee is currently $75. I did this 18 years ago for MUCH less, so I'm happy with the Va permanent trailer registration. I register my boat in MD since MD waters is where I primarily use it. I keep my trailer/boat parked in my driveway in Va.