Loaded old boat containing large case (7)
I believe the answer is:
Here is my best explanation:
'loaded' is the definition.
'old boat containing large case' is the subsidiary indication.
'old' becomes 'o'.
'boat' becomes 'punt' (I've seen this in other clues**).
'containing' is an insertion indicator.
'case' says to hollow out the word (remove centre letters).
'large' with its middle taken out is 'le'.
'punt' placed around 'le' is 'pulent'.
(Other definitions for opulent that I've seen before include "Rolling", "'Loaded'", "Rich, luxuriant", "'Rich, luxurious (7)'", "Wealthy or lavish", "Wealthy or luxuriant", "Wealthy, possessing riches", "'Rich, sumptuous (7)'", "Ostentatiously costly and luxurious" and "Lavish".)