As they "might" have said in The Treasure of the Sierra Madre; "Studs, we ain't got no stinkin' studs".
About 99% of the trailer owners on this site have molded
fiberglass trailers, all built without studs, and none big enough to have to worry about needing a second a/c for the bedroom (LOL)
The technique I have used is to cut a 1" hole in the area I wanted to explore and then use that to look around inside. If it proved to not work out I could always stick a small 4" diameter vent cover over my boo-boo.
You might get better information and help on a site for your make trailer and/or on sites for what we refer to as "stick-built" trailers.
That said, I once tried to use a stud finder and it just kept pointing at moi! (LOL)