Damn Bob, that's just cruel
A suggestion for you if you ever do another for a masking solution,
https://www.google.com.au/search?q=cling+wrap&client=firefox-a&hs=msy&rls=org.mozilla:en-US

fficial&tbm=isch&tbo=u&source=univ&sa=X&ei=I3iwUuuYEKGuiAem-4Bw&ved=0CHAQsAQ&biw=1255&bih=875#facrc=_&imgdii=_&imgrc=-WJHU4It_8XC2M%3A%3B6r0H_-KzYWRvlM%3Bhttp%253A%252F%252Fwww.glad.com%252Fimages%252Fproducts%252FGLD_CW_100sqft_frt_0512_VS.png%3Bhttp%253A%252F%252Fwww.glad.com%252Ffood-storage%252Fplastic-wrap%252Fpress-n-seal%252F%3B400%3B262
you can pull this tight around the areas and hold the join with regular mask tape not sticking it to the Alclad, this should solve your paint lift.
At a loss why the humbrol caused that severe cracking, one would look at the Future top coat not liking the thinner, i use Tamiya thinners for Humbrol, but have never sprayed paint over Future.
When you are ready, test it, alclad painted plastic strip primed the same as you did, half futured half not, segment the strip then put one drop of Humbrol thinner, one drop Tamiya thinner on each segment and see which gives that result.
Hope you work it out as that 47 was looking sweet.