At 7.5 inches tall, the BOAT37W is one of the shallowest heavy-duty tanks Ronco molds - 13 gallons flattened into a 29.75 x 16 inch panel that slides under bunks, cockpit soles, and cabin steps where headroom is measured in single inches. When the constraint is height, capacity comes from area, and this molding is all area.
Shallow does not mean light-built: this is an H.D. shell with the thick marine wall, molded in FDA-compliant polyethylene rated for potable supply. Ronco has made these in Tustin, California since 1974, and every tank gets its fittings installed per order - spin-welded or thread-mounted at the exact points you mark. Print the drawing below, plot your connections with the on-page fitting planner, and it ships welded to your layout.
A full load is about 108 lb spread across the wide bottom panel, an easy structural ask as long as the shelf beneath is continuous. Compare low-profile shapes in boat tanks, or view the entire line on the Ronco Plastics hub. OneSource Plastics is an authorized Ronco Plastics dealer.