As far as the lining is concerned it is not stainless steel it is aluminum. And it is inserted into the base of the tube and not the screw off lid. I would remove it as I did on mine as chemicals would seep in behind and it also shortens the diameter of the tube making it borderline for an 8/10 sheet of film. As far as light tight, no they are not at all. As far as coatings go there are different ways to approach this(this is my field of expertise). A good washing AND scrubbing with a stiff bristled brush using a detergent or TSP and a good rinse to follow. This will get the hand oils and grunge off from sitting in a welding supply house. A good wiping down with a WET rag of laquer thinner will take off any other oils/residues and etch the plastic. Then a good quality spray paint(I like Krylon) two coats will make the tube light tight. Sounds like allot of work on paper but an hour start to finish will due. As far as durability goes we are putting them in a tray of water so there is not allot of wear. Now when there is more than one tube in the water tray they will touch so the paint will need to cure down a bit to get hard hard. This will take a little time and till it does I would be gentle when using more than one at a time. I also groung off the little tab on the screw off lid on top so it sits flush on my counter. As far as the light tight thing goes they transmitted light from outside but they may be fine under a safelight if you didn't want to paint them. I also taped off the threads from getting paint on them.