Insane, having a fossil-fuel vehicle in this island (10)
I believe the answer is:
madagascar
'this island' is the definition.
(island nation)
'insane having a fossil-fuel vehicle' is the wordplay.
'insane' becomes 'mad' (similar in meaning).
'having' means one lot of letters go next to another.
'fossil-fuel' becomes 'gas' (gas is a fossil fuel).
'vehicle' becomes 'car' (car is a kind of vehicle).
'mad'+'a'+'gas'+'car'='MADAGASCAR'
'in' is the link.
(Other definitions for madagascar that I've seen before include "foreign location" , "Large island off the east coast of Africa" , "Part of Africa" , "Island republic in the Indian Ocean" , "Island nation" .)