Diy Roof Rack Water Tank . If you are looking for ute water tank ideas, you may have seen the toolboxes that you can purchase that sit under the tray, but either side of rear wheels (where the mud guards bolt onto). 5.2 diy rooftop bike rack/bicycle roof rack ideas. A Pvc Water Tank on the Roof Racks from www.4wdingaustralia.com So 30 gallons will be 15 foot (a little less than 30 galls) This rooftop deck was built in 2019, so lumber prices will vary, but this is still a great diy van rooftop deck idea for those that want to do this on the cheap! My idea is to build a trailer top water storage tank seining that there is un used space between the trailer top tent and the opening to slide in a table.