More than enough length in inside of camper (5)
I believe the answer is:
ample
'more than enough' is the definition.
(I've seen this in another clue)
'length in inside of camper' is the wordplay.
'length' becomes 'l' (abbreviation in geometry).
'in' is an insertion indicator.
'inside of' says to take the centre.
The central letters of 'camper' are 'ampe'.
'l' inserted within 'ampe' is 'AMPLE'.
(Other definitions for ample that I've seen before include "Quite sufficient, more than enough" , "Large enough" , "Spacious" , "Fairly large" , "Easily sufficient" .)