All maintenance penalties stack. If you're low on fuel, in red zones and damaged ... it is all multipliers, in that order. Fuel -> Red Zone -> Damage
I've seen, just one ships in extended Red Zone battles push Ship Maintenance up over 160% ... people sometimes blame politics for the economic slumps that could very well be corrected with better Fleet Command.
You can check this number in "Player Summary"
maybe you should do more detailed help files? in st damage has big impact on water-fuel usage, but here we have 'maintain cost'. before you post this i also didnt know that those variables have impact on maintain cost in $
now your information shows how getting bunch of fighters + cariers is a long term lower maintain cost fleet.