excellent! thank you for the responses! I actually think I have some marine grade polyurethane laying around.
for flashing, on the left hive, so there’s no way expand upwards after you do that, right? That’s the topmost super on that hive, forever, right?
For the shingles, are you meaning you will attach the flashing to the underside of the shingles or are you going to attach it the top perimeter of the frame, and then re-screw the shingles back on?
PS, i love all the support here!
Nope, that flashing is just on the roof. You can add another box under the roof, put your inner cover on top of that, and make your hive 25 boxes tall if you want! 
I will attach it to the frame using screws through the shingles. May need some caulking too, I will only know when I have done it. The major issue will be marking the existing screw holes accurately. I have an impact punch, so that should help. I have a roofing expert friend, so I may call on him if needed.
don’t give up on catching a swarm: it is very easy and rewarding. See if you an list an add on a local classified (graigs list?) offering to remove bee swarms. If it’s swarm season where you are chances are you will get a call. There are a lot of videos on youtube that show how to go about the capture.