The VIN numbers are located on the tongue of the trailer frame. They are not normally anywhere on the
fiberglass unless for some reason a manufacturer created a custom plate or the department of transportation issued a special replacement VIN and gave the owner a sticker or stamped metal plate to attach to the RV.
If you can't locate a VIN number you can contact your department of transportation for your state or province to arrange for a replacement VIN number to be assigned to it.
You can see in various places on the internet what a VIN number looks like and what the code means. The later VIN numbers have 17 characters (that is the current standard), the string of characters will be a mix of numbers and letters but earlier VIN numbers have fewer characters, such as my 1980 Sunrader which has only 13 characters.