Nice use of a balck iron cap. Did you dimple the stove so the screws would be able to grip the stove better? On my Chubby Sr I have a cap system and I drilled the cap and the stove, then tapped the stove holes instead of the cap. The cap I used is SS and the center portion is removable so I can replace it if needed. Permatex makes a high temp rtv silicone in black, you could use this to make sure your cap has a positive seal to the stove. Keep us posted on the durability of your new cap design or any changes you decide to make.
Sorry, I had to shut down the Jr and refrain from burning it outside. The local community put a petition together to ban my burning the stove outside even though I had the redneck seal of approval for my hearth. It became just too large of a tourist attraction leading to large traffic jams in the local village and thousands of people walking the two miles from the village on the main highway to my home. I pleaded my case and even pointed out that I was helping the global economy and my neighbors in Canada not to mention international relations.
I even used the angle that the stove was providing a source of heat for local wild life, preventing the needless death of poor small and large animals from the extreme cold temps. Still no joy, it didn't matter that the history channel was on location to film a documentary about the Jr and my redneck hearth. So, the stove now sits inside on display with my other coal burners I have in my collection. If you can get our newly re-elected president to give my local community some federal funds for road construction, parking, walking paths to my house and such, I will be able to put the Jr back outside and again help you out with your cold temps and heating bills. I will keep fighting for us, I'm currently looking for a loophole in the local laws. I'll keep you posted.