How heavy is your trailer? I know you aren't going to tie right away... but just for public input, I would be ~very reluctant to tie to it when not attached to the truck. a hard pulling horse might be able to move it.
Oh I wouldn't tie a horse to a trailer not hooked to a truck:). I saw a horse drag an unhooked trailer across my front yard one time. It was mine. The truck I use to pull the trailer, isn't getting used much now so I could just leave it out there hooked up all the time.
Becky