shock covers bad?

I use on on my rear shock to keep it clean because it normally gets like an inch thick coat of oil from the chain after awhile

and ive never had any probs...
 
They should not rust the shock but i would just take them off when you clean your quad so that way you know they will not rust them out
 
I spray the hell out of my shock with Wd-40, then put the shock cover on. Every once in a great while I remove my shock cover and do it again. It works great,.