A good way to do it is with a weak torque rod plus rare earth magnets as per my posts on these pages (some of them before the particular post that shows up first):
Note that you can adjust the power of the magnets by using either round or flat head screws, or by adding tape to the magnet. The screws let you adjust exactly where the spoiler blade stops. Put the screws in, put the magnets on top of the screws, put glue on the magnets, and lower the spoiler blade onto them for exact positioning of the magnets. This method is easy to do.
The rubber band system can be fine, but it puts a side load on the hinge, and if you're using tape that creeps, after a while it bottoms out on one side of the spoiler bay.
Spoilers are worth a bit of trouble to get just right.