Re: I-28 Vinyl Headliner Replacement
An interesting approach 510. I considered much the same thing except for your ingenious treatment of the aft corners of the cabin trunk. I backed off this approach mostly because I could never figure out how to deal with condensation between the headliner and cabin. Up here in the soggy Northwest, I have seen it raining inside my boat even when I left a ceramic heater to try and keep things dry. Also my experience with FRP and similar materials in suspended horizontal applications has not been good. I once used the grooved and primed version on one of my exterior porch ceilings and the panels sagged between the 16" joists. I forgot that these materials absorb atmospheric water and are plastic in the sense that they will deform over time from their own weight if unsupported. These problems could be solved by painting the back sides of the panels, using closely spaced attachments, ventilation holes through the edge trim, and gluing 1/2" Styrofoam to the overhead cabin fiberglass. This still leaves the issue of access should a failure or change to the blocks and cleats through-bolted through the deck require access. However, I'm thinking I may be solving a problem which doesn't apply to you in your location.
Because I already own one of those handy-dandy Sailrite industrial sewing machines and can more or less put two seams together, I have opted to sew up a new headliner using the old as a pattern. I will use the above-mentioned Styrofoam, S.S. or Monel staples, mahogany trim to replace the trailer trash trim, and a breathable fabric. Of course my plans rarely survive contact with reality but I will try and keep you posted on the project if you will do the same for me. Thanks.