Lacelady

This last picture shows rough placement of the gussets. The seam needs to be facing up, so that they fold nicely when you want to close the box. Sticking these in place is a little tricky, but not too bad. In order to get the fold of the gussets as near to the top of your box sides, glue down a tiny corner, so that it isn't sticking out beyond the top of the box side. Glue them in pairs to ONE box side, the excess will lay on inside of the box base, and will get covered up once the base lining goes in. Glue pairs of gussets to ALTERNATE box sides, so that you can hold them in place with pegs to dry. Then you can cover these alternate sides with the lining sides that have gathered pockets. Use the PVA glue for this, as it's a little stronger, and peg/pin in place where you can.

Once they are dry, then glueing the other sides of the gussets to the other alternate box sides is a little harder, and needs the odd pin and peg wherever you can manage it, plus a little judicious propping because at this point your box will no longer lay flat. The lining sides with the gathered strips cover these gussets and box sides.