They were joined at the scene between junction 8 and junction 7 by three crews from Hightown, Southampton, after a call for assistance just before 11.30am.
A spokesperson for Hampshire Fire and Rescue said: ‘The campervan seems to have been completely destroyed.
‘There are no signs of injury and the fire was extinguished by 12.15pm.’
Barry Barnes was travelling on the M27 towards Portsmouth when he approached black smoke coming from the other side of the motorway.
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He said: ‘There were flames coming out of the campervan’s window.’