I use the CIPA type slip on mirrors.. You can buy almost anywhere now, even WalMart. I love them since once they are adjusted, you can take them off and then put them back on and not have to readjust.
I have an Undercover Flex cover on my truck. It is a trifold like RoyB shows, just a different brand. Love that I can leave it on and fold with 1/3 covered and haul something too tall to fit under it. I also can stand upright and use all of bed when I am hauling limbs, etc. Love the fact that I don't have to remove cover to use the bed.