Sounds to me like big galvanized lag bolts would be your best bet. (haha)

I'd almost vote for 5200, but even though it is advertised as an adhesive
caulk, it is designed to be backed up with screws or other fasteners. The
Liquid Nails is a good bet, but it will harden up pretty good over time.
But at least it's designed to work alone. Got any handrails on the roof?
If so, maybe you can use 5200 and run screws into the handrails (if wood) or
bolts (if metal)? The 5200 may work alone if you give the wood good
coverage. It never gets rock hard, and it's a 'female dog' to remove later
should you ever need to, and be prepared to leave it clamped up for the
better part of a month if you want to rely on it when you release those
shower curtain rods (good idea BTW). Gorilla Glue works too, but again
....like Liquid Nails, it'll harden up over time. Both will fill gaps
reasonably. The true glues will likely do just what your first glue did
....hold up quite well, but harden up and be tough to remove later on if you
end up doing this job again. The 5200 flexes with temperature and moisture
better, is a PITA to remove, but I've never used it alone ...as an adhesive.

Good luck and let us know what you go with.

Brian



"1088" wrote in message
...
Day of sun, day of rain, day of sun, day of rain,.. I'm back inside
the breathtakingly spacious cabin of my 23' yacht with it's many
luxury appointments getting ready to stick up some stained plywood
panels I made. It's 3mil 1088 Okume ply. (hence the rakish moniker for
this phase of my "refit".)
The back of the old stuff was just smeared in a haphazard pattern with
a pale yellow paste that dried hard as iron and has to be ground off
with diligence and firm language wearing haz-mat headgear. The boat
was built at Cowes.
So,.. I'm gluing plywood to rough, scabby old fiberglass. What would
be easy to apply for a person working alone? I use telescoping plastic
shower curtain rods for clamps, or I guess it would be the reverse of
clamps. Liquid nails? 5200, 4200, sikoflex 216, 61a? Cheap, good and
readily available would be great but if anything buzzes or rattles
when the engine runs I will jump overboard.
Ok, the spell check is complete, I had 6 errors.