I have used both the tonneau and Caps in different styles. I had a one piece hard plastic tonneau and will never do that set up again! It had a brackets that made it quickly removable but for those random shopping trips and buy a large item I didn't like riding around with it open. I had a few different type of vinyl ones and the ones with Velcro down the side (the rest can be a pain in cold weather).
I currently have a fiberglass cap on my truck and it is heavy. Nice part is I dont ever plan on getting a fifth wheel and have a utility trailer so I dont have to remove it. Have a thule rack system on top for bikes or kayaks/canoe. The window next to the truck cab even folds down so you can wash the glass. My dad has a aluminium one that even on an 8ft bed is not bad to remove and install with 2 people. It doesn't look as nice as the fiberglass but it was cheaper.
From what I know of your situation I would recommend a hard roll up or folding tonneau. Not 100% weather proof but do a good real good job. You also get the security and can add a fifth wheel hitch. They are also cheaper than caps.