I have added treated lumber deck boards to my lifts. They run the full length of the lift. It is a cheap sort of safety step. I would not suggest putting a great deal of weight on the area as it isn't designed as a load bearing surface according to the manufacturers. The single board makes it hard to fall between the dock and the boat.
Boat covers are not water proof but they keep most of the water out of the boat though which is why my boat has a cover and canopy. WARNING: A canopy can turn into a sail so when the boat is not on the lift a good wind may move the lift along ways. I install my canopy on the lift after the boat is in the lake for the ski season. I remove it when the boat is taken out in the late fall. Installation tip: It is easier to stand on the boat raised up on the lift and install the cover than any other way I have tried. I use plastic wire ties to secure the canopy to the frame. I tend to lose the re-useable ones.