The bolts down lid would be for something like a gas station to prevent tampering. (I've never sold one) ST743SB
The ST743SD insulated tank is for areas of high humidity and very cold water.
I sell a few of these in Alaska.
Normally I sell either the ST743S or the ST743E tanks.
The (Gwyneth) Drake II has the double cyclone and Sanagloss with the taller bowl.
It's a nice setup for someone that wants a taller bowl.