Thank You. It's very snug. I have to nudge my way around it to loosen it enough before comes off.
Ehhh... I would be more than a little uncomfortable with this.
What happens at minute 31? Or 40? Or even later? Are you absolutely 100% sure the adhesive won't begin to soften and fail on the inside of a black plastic cover as the Sun beats down on the other side? Are you sure the dust cover itself won't fall off?
I don't mean to sound like a curmudgeon, but... your eyesight is at stake.
I would look for something that is far more secure than spray adhesive making contact with only one side of the filter film. I'm thinking of the kind of sandwiched DIY filter cell that Baader describes on their AstroSolar.com website.
This is why I'm doing the tests. It hasn't gotten really really warm here yet a but it's been in the the 70s almost 80s already but not much. During the summer it'll get into the 80s and maybe the 90s with a decent amount of humidity. I already have a well-built, long tested (10 years) solar filter for my little 70 mm refractor so I could easily just use that. As far as the dust cover falling off, it fits so snuggly I usually have to pry it off from around the edge before it even comes loose. So that it isn't an issue at all. But as the temperatures rise during the season I will do more tests with it on the scope without viewing through it and over time test the adhesive which is quite a strong bond that I use for nearly everything so it should be OK. If there becomes any question of safety, I will do the other way because I do have enough to create a full-aperture filter with cardboard as it "should" be done.
You seem to be on the right track with a proper attitude, but sometimes it's easy to overthink the details.
I would strongly suggest that you find a better method.
If you can nudge it to come off, then assume it will.
Adhesive tape is not a secure method, and gravity is your enemy here.
I would suggest that you find another dust cap for your aperture opening, cut out the centre bit, and sandwich the film between the dust cover and the front collar of the dust cap.
Much like a collared full aperture cover (make one if you have the film!), it puts the film in the front of everything else.
It sounds like the caps are snug but... try to use some Velcro tape at this point for your new "collar" , and make sure that you secure the larger dust cap to your main scope as well.
Solar observers generally have Velcro dots and strips hanging off of their scopes and dew shields for just this reason. Not attractive, but necessary.
Always assume something will go wrong, check and check again.
Sorry to sound like I'm preaching , but we have to be careful out there.
Besides, you'll want to share what your seeing, and you will benefit from the longer f/l with your new mask.
Hope this helps.