The container should sit like this. You may need to remove the lugs from the bottom part of the container (1 in each corner) to allow the container to sit flat on the wagon bed.
I use Krystal Clear to glue the base of the container inside the container permanently. Once dry I then use Krystal Clear to glue the container onto the wagon bed. PVA and super glue can be used for this as an alternative however be warned some glues will discolour the wagon and container.