"So, is there a solution that doesn't involve PVC pipe or vice grips?
Stronger struts? Extra struts?"

No. I have a 5 gal. gas can (full), Gary Lee rack system, bike mounted
on it most trips so  it's not just unreasonable to believe there is a
strut/s that would hold the hatch up, also not possible. The Gary Lee
racks always come with the PVC tube on one of the struts but I also
bring along a mechanics hood strut clamp that has the orange tag on it
as reminder, to more equally distribute the load. This all works great
AFAIC. My Gary Lee spare tire carrier is of the swing-away variety.

Bob Stevens
'87 Syncro Westy