Long-distance travellers in camp seen misbehaving (8)
I believe the answer is:
spacemen
'long-distance travellers' is the definition.
'camp seen misbehaving' is the wordplay.
'misbehaving' is an anagram indicator.
'camp'+'seen'='campseen'
'campseen' with letters rearranged gives 'SPACEMEN'.
'in' is the link.
(Other definitions for spacemen that I've seen before include "High fliers" , "long-distance travellers?" , "Astronauts" , "Adventurous travellers" , "they have a high trajectory" .)