I have long felt like the emergence of unmanned surface vessels as warships might lead to weapons and sensors that would also fit nicely on Coast Guard cutters including containerized systems.
Chuck Hill's CG Blog
I have long felt like the emergence of unmanned surface vessels as warships might lead to weapons and sensors that would also fit nicely on Coast Guard cutters including containerized systems.
Chuck Hill's CG Blog 
The concept of weapons in a container are good for things like cargo ships, auxiliaries, T-ATS, or other ships that have lots of deck space, and power available. This does not describe a frigate or any other small surface combatant.
To continue the analysis . . . extra weight sitting above the waterline on a small surface combatant is never a good idea particularly if it might enjoy heavy weather. The smaller the ship the more impactful any mass added above the waterline is.
If one has the options and the time weapons systems should be designed within the platform saving the precious extra weight of the container, and that weapon system mass be ‘programmed in’ as efficiently and effectively as possible. Containers on deck where deck space is not generous, excess power even less . . . is just asking for trouble when adding weight topside, and is never good for stability. Anyone suggesting such an option either are not qualified, or have watched too many movies.