SailorBoy, you are a very knowledgeable poster, so I hesitate, but.....
Back off for a minute. Take a more holistic look at it, because I know you have been installing good seals. If the seals are not really sealing, you can test them by temporary caulking on the outside, and in addition you should already have seen frost at the point where outside air is getting in.
With those two checks, then you know that moist air is getting in somewhere, but it's not your seal. Is it coming in at the copper pipes? Is the box itself leaking at a seam? Where do you first see frost if you run it sealed and empty? It may reveal itself by frosting up at the entrance.
Frustrating. Been there, but not for refrigeration
. I most often solve the frustrating ones when I unfocus from hitting my head
on a no-working solution and look at the broader picture.
Good luck with it. Thanks for all your help for people like me on this forum.