Here is my rough sketch of the covenant as it existed around the time of your Gauntlets.
The formal name of the Covenant is Hodopoion, but after many years it has become known as Carnacis. The original name came from the Criamon that founded the place as one of the first Hermetic covenants in deeply pagan lands. The later from the nearby intensely magical sight of Carnac.
Physically, the Covenant is on the north-western arm of land that defines the Gulf of Morbihan. The land is wet and marshy, but one of the few really magical places in Normandy. You are very near Carnac (to the west) and Auray (to the North). The main Covenant building is a large, white marbled Edifice, over 100 feet high at the top of the dome. The covenant is huge by local standards. Its aura is vast, covering nearly a square mile. The main covenant building is on a small hill, overlooking the Atlantic ocean. a road stretches to the north east to a small village about a half-mile away. This is the home of the covenfolk, craftsman, etc. Near the village is a cluster of conjured towers that hold junior magi's sancta, as well as supplies and gear for the covenant. Below the main structure is a large cavern structure that few have seen.
The covenant itself goes back to shortly after the Founding.
The covenant has a successful trading concern based out of Vannes. The magi rarely visit the city, and trusted mundane agents manage a fleet of over a dozen merchant ships that travel all over Europe. When a magi needs to travel, he simply rides along the merchant vessel as a passenger. The covenant's grogs do double duty as pirates. Every now and again one of the merchant ships will sail under the pirate flag, suing magic to disguise its nature. The profit comes not just from the prizes the pirates take- but the fact that it is always the covenant's competitors that get attacked. Finally, on some trips the trading vessels carry pounds of conjured silver to far off ports, where wares and cargo are purchased- avoiding the damaging effects of dumping magically created coin into the local economy. Both the piracy and creation of money are criminal endeavors (one mundane, and one a Low hermetic crime).
There is no concealing such a covenant and the magi do not try. They have friendly relations via mundane agents with the local cities of Aurey and Vannes. The lord of the region is Comte de Morbihan and while he is not hostile to the magi, he is wary of them and the power they wield. While they have not taken the knee, a local knight (Sir Luc) has, and the Comte has "generously granted" the land the covenant sits on to Sir Luc. Sir Luc is actually one of the ruling council in mystical disguise. The Comte frequently requests stealthy aid from the covenant, and more of then than not receives it. The Comte's feudal obligation runs up to Peter the Duke (or Count, depending on who you ask) of Brittany.
Hermetic politics to follow...