I designed this bag clip to keep my filament spools away from moisture and the seal seems pretty airtight to me. 
It is a very simple model with only three parts, which can be easily glued together with super glue (make sure that the glue is fully dried before trying to seal a bag).
The model can be easily printed on the build plate of the Centauri (or on the Bambu Lab X1C)

I designed it to be printed at high speed taking into account some inaccuracy in the interlocking parts, so the play between them might be too large and they might not fit together perfectly — but nothing that a bit of super glue can’t fix.