F#cking love your bike, I used ammo boxes as well, not much for storage but I can pick up a bottle of whiskey on my way home...lol. My bike has been described as steampunk, mad max, water world, scrap iron and one person even said "Looks like a Kawi got a$$ raped by a Transformer without lube!" That last one is my favorite...lol.
Other than the cost of the bike ( a long story about my ex wife... her standards... my credit ), I have about $600 into the chop and that includes most of the materials to build a springer front end out of some hex stock I found at a junk yard. Just like you a 110 flux core mig welder and about $2000 worth of whiskey and beer consumed in the design process.
Are you set on port holes?? There are tons of different styles of sight glasses used in pressure vessels in the petroleum processes and such. I used to work in the oil patch and have seen hundreds of such items, but you also find them in scrap yards and no one cares about them. They are more worried about the scrap metal than what is attached to it, and you can get them cheap. Most of industrial sector will have something similar.
Here is a link to some new ones but you might see something you like.
Keep us up to date on your build!!