If you are making multiple asides, the standard approach is to use square brackets within the first parentheses, not double parentheses.
e.g.
The dildo was menacing and enormous (likely the biggest I have ever used [nearly 4 feet]).
If you are making multiple asides, the standard approach is to use square brackets within the first parentheses, not double parentheses.
e.g.
The dildo was menacing and enormous (likely the biggest I have ever used [nearly 4 feet]).