One regularly uncovered chap in barrel turning up (6)
I believe the answer is:
nudist
'one regularly uncovered' is the definition.
(someone who doesn't wear clothes)
'chap in barrel turning up' is the wordplay.
'chap' becomes 'sid' (man's name).
'in' indicates putting letters inside.
'barrel' becomes 'tun' (tun is a kind of barrel).
'turning up' says the letters should be written in reverse.
'sid' going within 'tun' is 'tsidun'.
'tsidun' in reverse letter order is 'NUDIST'.
(Other definitions for nudist that I've seen before include "One not covered" , "Naturist" , "One forsaking clothes" , "S/he prefers to be naked" , "Streaker?" .)