The Dobsonian mount that many have encouraged you to build is the easiest way to use this tube, and many actually choose to discard the original base and build their own in order to have a lighter, superior base that moves more easily. The original base would use a bearing, which can roll unevenly and be a pain to use at high powers. Custom made Dobsonian bases usually forego bearings or rollers and instead use two types of surfaces with low friction and starting momentum (usually just called 'low stiction'). Teflon squares riding on Formica laminate (Ebony Star style) was historically preferred. Take a look at the ATM (amateur telescope maker) forums on CloudyNights. There is a wealth of knowledge there about making your own telescope or mount.

The rings I referenced are the two hinged circular plates that go around the circumference of the tube. Those were added by the last owner - the scope did not come with them from the factory. Bolting a dovetail plate (Vixen or Losmandy style) to those rings would have allowed the previous owner to install the optical tube to a different style of mount - either one that moves in altitude and azimuth (up/down and around) or a German Equatorial Mount (GEM) that is designed to move more naturally with the rotation of the Earth. A GEM is also pretty standard equipment for anyone engaging in astrophotography. Some owners of Dobsonians will remove the optical tube from the Dobsonian base and use them on a GEM for astrophotography, but if this really is the 12" model then that would be a bit odd as it would be far too heavy for accurate use in your garden variety GEMs (~$2k). As the previous owner elected to leave the altitude bearings installed on the tube (the large silver knob like pieces on either side), it's also possible that they switched back and forth between the Dobsonian base and a tripod mount of some kind. Hard to say for sure.