Trans-cyclooctene is isolatable at room temperature.
Trans-cycloheptene is also known at low temperature.
Ab Initio Conformational Analysis of trans-Cyclohexene (1995) says that there is spectroscopic evidence of the existence of trans-Cyclohexene, but that trans-cyclopentene hasn't been studied.
So I'm looking for any further information on trans-cyclopentene, trans-cyclobutene or trans-cyclopropene, particularly whether any of these have been theoretically calculated as (or ruled out as) corresponding to a local potential energy minimum.
