Winkler was afaik never a midshipman.
He was a ship's boy, and/or a young recruit. However definitely of lower classes, and destined to be a crew member, not officer.
The class distinction was very difficult to overcome. Those young volunteers who were of high clases, got then (after some time as shipboy, which could even been nominal service) the appointments to midshipmen. Low-class boys remainen ship's boys and servants, and often were advanced to seaman status when aging.
Only rare cases, a servant-class person could make to midshipman rank;
and in only rare cases, a seaman could make it to officership, i.e become lieutenant.
It's like there was a fast trach to officership for higher-class young men, they being promoted towards officer corps usually via midshipman service. It was not usually open to anyone else than to those who were of educated families....
It is unclear to me whether Winkler is in the payroll of the navy or in George's personal payroll.
However, in practical terms, this is not important for now. because, as servant-class crew member, Winkler is anyway quite plausibly posted as George's permanent personal servant. This will not change in the foreseeable future, because george holds a position (actually yet a higher position) where he is entitled to have personal servant.
On the other hand, if Winkler technically resigned from the navy and entered into George's personal payroll, the location of his service is for now the very same anyway.
I tend to believe (of these two alternatives) that Winkler remains in the navy payroll.
If so, his rank is one of a lowly crewmember.
Winkler presumably is not, nor has ever been, in middie quarters inhabitant.
Nor uniformed as middie.
Crewmembers did not have that much of an uniform anyway in those days. Read how they made some clothes to themselves from the distributed fabric.
There is no reason to believe that Winkler would have any sort of dress uniform. Officially.
(now, if he happens to be a uniform aficionado, he could have devised quite a nice uniform for his...)