I don't rotate my ships, that's why I call myself lazy 3-2A leveling, if you want to do something similar to mine (lazy yet still decently effective) then just use a Maruyu (if you have one) and let her be the sub, she come back red, then stick her into dock, only takes like 5 minutes, sortie again. Whilst you're waiting for that 5 minute, fatigue will get lowered, you can do something else like read a manga...etc, this way you barely notice any fatigue if any at all.
After 3-2, most map actually have some minor branching rules just like events, so you might want to check them out before sortieing to ensure your higher chance of success.