Hi Bud,
In a word 'tricky'.
Threading the belts through the various photo-etch buckles and fittings is not easy, but I think worth the effort.
When assembling the seat straps, use CA adhesive.
To avoid the adhesive soaking through the seat belts and sticking to the working surface, assemble the belts on a shiny surface, such as tile.
When holding down the belt joints to allow the adhesive to set, keep the belt moving over the shiny surface, which should stop the adhesive sticking the belt to the working surface.
Mike