Is the wood punky where you're trying to attach the gas spring? It wouldn't take much water to rot the immediate area around the screw holes sufficiently to keep them from having much strength, even if the wall in general is fine.
Is the other end of the lift in question binding or bent at an odd angle, putting unusual stresses on the attachment?
If you can get access to the back relatively easily (and doubly so if it's not an interior finished wall that you're going to see constantly), I'd see about removing some of the presumed foam laminate sandwich from the area and replacing it with a backer of plywood or something similar, glued to the thin Luan or whatever the outer skin is adhered to. Obviously use sufficiently long mounting screws to get a good bite in the plywood. Of course, this might not be practical depending on the wall construction; I'm certainly no expert on all the possible variations out there.
