How can a designer ensure the longest life for a Lift Support in an application?

Orient the support "shaft down". this will continually lubricate the seal and shaft and reduce permeation through the seal.

Utilize the largest gas volume possible in the support. In general, use the minimum stroke required with the largest body possible. In a support with a large gas volume, small gas losses are imperceptible in the output force.
The temperature of the Lift Support should remain well within the temperature limit s. If temperature extremes will be encountered, it should be for a short duration and the support should not be cycled while at the extremes.
Utilize the highest force Lift Support possible that still provides acceptable handle loads for the application. This will allow for some force loss without the loss of function of the application.
Provide multiple mounting locations so that the support can be moved to accommodate for force loss as the support ages.