Yes, these Fiberglass Reinforced Plastic "FRP" tanks are made for potable hot water up to 180F, are food grade inside like a sink, and have stood up water-tight for 20 years in Canada.
Cost for 360 USG tank is $1198, and for the 540 USG is $1798 (2045 liter / 450 Imp. gal.)
Heat loss is not generally understood in solar. German scientists show with 10m2 collectors, insulated pipe heat loss cancels 2 m2 and tank heat loss another 2.5 m2, which is nearly half the heat input. By comparison, uninsulated pipes is triple the figure, making the system lose 8.5 of 10 heat units.
That is far less than adding up a row of 4.5 120 gallon tanks, and has 83% less side and top surface area to radiate heat loss, more like 100% taking into account heat loss with manifold pipes on multiple tanks. (540 USG tank vol=72 ft3, so 120 USG = 4.5 tanks to make 72 ft3, with side and top area of 156.7 ft2 vs. 85.6 ft2 = 1.83:1 )
They ship "cupped" to reduce space and expense. Each section is a manageable 54 pounds.
We have an enginneer drawing at the bottom of this page:
Solaris Manufacturing - Products