If the holes are pretty small, which most portholes in popular scales are, you might try clear lacquer. It is a bit more shiney than those PVA glues.
Trying to replicate ship windows/porthole looks is very difficult. If it is supposed to be a specular reflection, then it will look gloss black except where you get a reflection of a bright light or object. This is very difficult to do with paint. We unconsiously are quite aware of our surroundings, and expect any reflecting surfaces to change what we see even if we move slightly. Hard to do with paint. Now, most of the time we display our ships indoors, where the brightness and contrast of our surrounding are much, much less than outdoors.
I usually finish open portholes and windows with those window materials like Micro Glaze. They will show some reflections of bright lights and such, but the problem is that there are few lights down at levels where you would see a specular reflection. If you want to really show the fact that there are windows or open portholes, I suspect putting lighting inside and a glazing material over the holes and windows. I have seen some beauties done this way. I have not done it myself, but the ready availabilty of LED lighting stuff these days is such I will be trying it soon. Think of something like the Titanic or other liner done that way- it should look spectacular.