Joining objects after box morph

Hello all
I was wondering why i cannot join thesebox (17.1 KB) objects, after using box morph
you can see there is a small gap between the objects if you zoom very close
I thought the objects should be touching their edges
Is this a tolarence problem?
Thanks for the help

The edges of your shape don’t quite touch the bounding box so I split the untrimmed surface with the box and all is well.

box (19.7 KB)

You didn’t mention anything about getting a ‘Closed Brep’ (“solid”) but just in case (yellow group):

box (22.8 KB)

Thank you so much Joseph
Best regards