I just finished mine. I replaced the rivits on a large flat table. I put the sealant on, on the same table. The gutter twisted and made reassembly a bear. IF I were to do it again I would do the sealant on the vehicle after assembly.
Also the head liner installed, I paid a "pro", he waded up excess headliner on top of the gutter rather than trimming it the way Toyota did originally. He ignored my instructions on how to do it and refused my request to help or be present. The extra fabric, not glued down, thank goodness, caused reassembly issues. So, I properly trimmed it, which went badly in one place.
People are so frustrating! : )