We get lots of questions around helping people identify a trailer they just bought or are thinking of buying. Here are some suggestions to identify your trailer.
First off, you need to use Google. If you can't find a reference to your trailer on Google, then you probably have a trailer that isn't a very popular brand. All of the popular brands have websites, user groups, yahoo groups, or forums of some such. This is because there is a demand for information because of their popularity and value. This doesn't mean you won't be able to find information, it will mean that you have a lot more work to do on our own. It doesn't mean your trailer isn't valuable, you might have a very rare trailer. But it does mean that finding documentation, floor plans, original equipment, parts, knowledgeable resources, etc is going to be difficult if not impossible.
Bring your trailer to a vintage trailer rally, there are lots of experts at these rallies that don't leverage the internet but might be able to recognize or help you identify your trailer.
Other options are to look in the Tin Can Tourists Yahoo Group for a trailer that is similar and if you find something we might be able to tell you what it is. While you are there, upload a couple pictures of your trailer and someone might be able to identify it. Provide as many details as possible.
The Tin Can Tourists Facebook Group is very active and helping people identify and learn about their trailers.
A good resource of trailer information is the RV/MH Museum http://www.rvmhhalloffame.org/ - maybe if you send them pictures and details, they might have an idea.
You need to find serial numbers, VIN, markings, makes/manufacturers of equipment, paperwork - anything that could be a clue. Here is video on uncovering VINs on tongues http://www.youtube.com/watch?v=DXT2LcXebCo&feature=youtube_gdata_player
Also - there are plenty of homebuilt trailers out there - you might have one. If so, your not going find any information on it. It could just be a custom one-of-a-kind!
Here is the best resource for getting copies of vintage trailer magazines, ads, and information: http://www.allmanufacturedhomes.com - Juergen Eichermueller - The definitive independent vintage recreational vehicle archive source!
Serial numbers are frequently found on the tongue rail on the passenger side. (Usually on top, but may be on the drivers side or the side of the rail). Use paint remover or sand lightly to uncover the numbers. The first two digits may be letters that identify your make, followed by the year, length and number of production. Example: Serial number (or VIN number): MR 57 25 123 is a Monterey, 1957, 25' number 123.
Here is a record of trailer names and the abbreviation you may find on an old title or registration: http://www.oregon.gov/ODOT/DMV/docs/VTRH/Chapter_N.pdf?ga=t
A wood screen door or free-standing stove often mean you have a pre-1960 trailer.
Teardrop wheel wells may be a Serro Scotty. Compare it to pictures here: http://www.serroscottycamperenthusiasts.com/