It would be cool if you could build your own sliding platform in that space. This way you wouldn't have to crawl in the get stuff out or at least stuff in-between the top of bed and under rack. Does the bed of your truck have some sort of tonneau cover or is it just an open bed?
My rig had a very annoying squealing noise coming from the fan belt area. Watched some YouTube videos for a fix and picked up a bottle of 303 Protectant from Amazon. Sprayed it on the underside of belt and around pully's and bamm no more sound. I am so happy that I can hear the normal engine...
Mike recently posted this video, which shows two water filtering products, one of them using a jerry can type container (sorry not Rotopax though)
Outdoor Water Purifier | GRAYL and LIFESAVER JERRY CAN - YouTube