So I have a 99, f350 extra cab 4x4. I was crawling under it yesterday and it dawned on me that there was a lot of unused space under the cab between the sides of the cab and the frame. My first thought was I could probably fit some 8” scedual 40 PVC “tanks‘“ down there, each about 5’ long. That would give something like 13 gallons per side. Or does any one make tanks that would fit? I’ve never seen any one use this space before, any ideas on us wing this space? The two pictures are looking forward from the end of the cab.