They are no problem i hear (the oem allooominum ones) and i have just fitted a HVA cover to replace a badly "pooohhed" mag cover.
It wasnt "perfect" and i had to drill out one bolt hole to get the line right. the pump cover holes were much shorter than the std so i had to get shorter bolts and i had to drill out the vent hole for the bigger tube.
But no corrosion??? uuubbeeeuutteee
!.
I've heard that painting the cover with a high powered 2pac paint can help life as well.
Enjoy