Interesting, I never knew there were different strengths available, though I
do recall seeing some "heavey duty" ones mentioned.
  I have a Yakima bike rack mounted on my rear hatch most of the time and I
often carry as many as three race bikes and up to six wheels on my hatch.
Probably ~100lbs, with the rack's weight.  So I needed a way to support the
hatch with the load on it. when just the rack is on, it still creeps down,
then slams shut sometimes.  I did that neat trick with the PVC over the
struts, which works great for when there are no bikes on.   For when the
rack is loaded or for very windy Gorge days (the hatch can blow up, the PVC
supports slip off the struts, the hatch slams shut, sometimes, in wind
gusts) I use a secondary support.  Being a 'direct dude' I took a piece of
oak and drilled a  1/4" hardwood dowel into one end with about 1/2"
protruding.  I cut this support stick at the right length to just slide into
the groove where the hatch weather stipping fits when the hatch is full
open.  So I open the hatch, with the load and take that stick out from under
my rear pad, stick the dowel-end intoa holeiin one corner of the bottom of
the hatch and then slide the other (bottom) end along the groove in the
body..starting from the center and pushing it out to the edge of the
opening..The fit keeps the stick (you could call it.."a tension-torsion
uni-directional carbon-based support structure" if 'stick' sounds too
mundane) in place and the hatch open.  Having a hatch to slam shut on your
backside while bent over the motor is not a good thing, don't ask......

  Don Hanson