After all the pieces were in place, I realized that the "coupler base" was missing.

The assembly manual says to call 1-800-444-3353, but they are closed so I will have to call them again tomorrow.
Has anyone ever had to call them about missing parts? Were they helpful?
This is a long shot, but would anyone happen to have a coupler base laying around? For reference, it is the boxy piece on top of the end of the tongue that the coupler gets bolted to....

Thanks in advance!