The B428 spreads 36 gallons across a 46 x 36 inch panel only 6 inches tall - a true underfloor tank, wide as a sheet of ply is deep and shallow enough to live between floor joists or under a raised RV floor. When headroom is the scarce resource, this format buys capacity from square footage instead.
Fresh water or gray/black waste is set by the fittings, not the mold; the B428 is a dual-role B-series shell like its marine siblings. On a 6 inch tall tank, think hard about where the outlet goes - put it at the low corner of your actual installed slope so the last gallons drain. Print the drawing below, mark every fitting location, and use the on-page fitting planner; Ronco spin-welds or thread-installs precisely to your marks.
The blank ships at 102 lb, and full it holds about 300 lb of water spread over the footprint, so it wants continuous support under the whole panel rather than rails at the edges. Molded in Tustin, California by Ronco, at this since 1974. Other shallow-profile options live in the RV water tank range, the holding tank range, and the boat tank range. OneSource Plastics is an authorized Ronco Plastics dealer.
Technical drawing: download the Ronco Plastics B428 dimensional drawing - print it to plan your install and mark exactly where you want fittings located; Ronco installs spin-weld or threaded fittings to your marked spec.
