I made the portholes which will be fitted to the superstructure using Brass & Copper rings,  I then fixed some miniature brass nuts in place to replicate the fasteners using Gorilla Superglue Gel & I used frosted acrylic sheet to simulate the glass. To finish them off I just need to add handles at the 6 o'clock position which I will fabricate using thin brass rod. Each porthole measures around 30mm diameter.

Click on Image below to enlarge