The installation is engineered using a cantilever system, sealed with silicon. The lubrication is done via a greased nipple or two.
After the initial capital outlay the design is considered fairly cheap to maintain , on the other hand the rest of the structure can incur a considerable cost with the ongoing upkeep required for it to function as desired, which for all in-tents and porpoises is usually undesirable in grandma's opinion.
Glad to be of assistance.
Malcolm.