Here is how an RVB407 actually gets ordered. You print the technical drawing below. You tape it to the bench, pull up your plumbing plan, and mark where the fill needs to enter, where the vent must rise, where the pump pickup wants to sit, and whether a sender port belongs on top. You run those marks through the fitting planner on this page. Then Ronco's plant in Tustin, California spin-welds or threads each fitting exactly there, and the large light-duty fresh water tank that arrives is already configured for your build - no drilling, no bulkhead improvisation, no compromise layout.
That workflow is the real product. The molding itself is one of the bigger blanks in the B-series at 147 pounds, translucent natural polyethylene, FDA compliant for drinking water, off tooling Ronco has run since 1974. The translucent wall doubles as a level gauge; the natural resin shows the water, and anything in it, honestly.
A tank in this class deserves a weight plan as much as a fitting plan. Water is 8.34 pounds per gallon, so place the tank low and over frame structure, and make sure the bay floor is continuous under it - light-duty moldings are specified for supported installations, which is exactly what a proper RV bay provides.
If this footprint is not your footprint, work through the RV water tanks or the full Ronco Plastics catalog, and sanity-check delivery cost with the freight estimator. OneSource Plastics is an authorized Ronco Plastics dealer.