Hi Erwan & Steve - I guess it might be worth a shot but it is pretty unlikely that boolean union will work where joining failed, for this type of "big bunch of open surfaces" type of thing.

Although it is possible for boolean union to manage the same job as join, it tries to do a lot of extra work with intersecting objects with one another, it is more focused on unioning 2 pieces that punch through each other (like 2 solids that push through each other) instead of open surfaces that share common open edges - that's what join is focused on.

- Michael