Thinking out loud here...
Does the prop have to be so long? It seems that the lid only needs
a little bit of help to support the added load of the bedmat...
...realizing that each has his own individual requirement for "lift".
Sorta like looking inside a fridge to see if the light went out when the door was closed but...
How much area in the trunk will be sacrificed for the prop when the lid is closed?
Have you looked into a shorter cylinder design and perhaps a "clamp-on" upper mount - for the curved hinge rail - that could be positioned along it in different locations for different lift requirements? (For example, clamping it at a lower position would take-up less space and might help to prevent any bent struts.)
I realize there are few options for the lower mount location, especially for a no-drilling/bolt-on solution. The driver's side has an area (way up inside - to the left of the spare) where there is a outward-curved area (sort of a "hump") where I tried to locate a mount (temporarily). I think the composite would have to be reinforced, or a mounting plate would have to be large enough to "spread-out" the force of the strut.
I then simply attached the other end of the prop to the exposed end of the spring. I didn't think of a clamp to the hinge-rail at that time.
Anyways, even with the bottom end of the strut just
wedged-in at that spot, and with the top-end attached to the spring, the lifting force was adequate, and the entire prop was completely away from anything in the trunk.
I wish I'd taken pics.

Maybe there's a pic of an empty trunk somewhere here in the ROC...
Thanks again,
FIG, for your continued interest in helping to find a solution.