Ours had a Century fiberglass cap on it when we bought it. That was a very nice high quality cap. Within a few months we sold it and got an Extang Solid Fold cover. We found the cap to be restrictive, couldn't stand up the bikes to keep them from getting banged up, couldn't haul loads that stand above the opening of the cap, couldn't have dirt or gravel dumped into the back, etc.
Our Solid Fold cover folds up to easily access the bed, is easily removed in a few minutes to carry our bikes or loading dirt, or what ever. Plus the cover locks (provided your gate has a lock) and no one can see what's inside, unlike most caps, which anyone can see inside. Those cheesy locks on the cap door aren't going to stop anyone from getting your genny or your bikes.
Everyone use their trucks differently that's why there's so many options. Caps don't work for me, but given what you want to put in your bed you may get a lot of benefit with a cap.