bed cover for '06 D cab

What are my options for covering my bed? I would like a hard cover that is lockable. Would I have to remove my bedside covers to mopunt it? Do they even come off? Can the hard covers be easily removed for hauling things?

I bought one from Xtang..it actually fits! I'm having a little trouble getting everything as straight as I want it, but I think that it will work out.