This question is a little tricky to answer, as I'm not totally sure what you mean by "mantua".

The mantua was first made in the late seventeenth century, as a very informal alternative to the previously normal two-piece gown. The two-piece gown consisted of a bodice (often boned) with sleeves and back-lacing, and a petticoat which could attach with ties to the waist of the bodice; the mantua was essentially an unboned long coat, open down to the bottom, that would fasten loosely and be worn over a separate petticoat. By the last quarter of the century, it had become a moderately fitted gown - the loose torso of the main fabric pleated to shape and sewn down to at least scraps of linen, at best a full lining - and was worn over stays to give the body the respectable, public-appropriate shape for everyday dress. Over roughly the first half of the eighteenth century, the gown that nearly all women in England and Anglo-America wore on a regular basis was the mantua, with continuous updates to its construction over the years. What connected the gown to its forbears was the continuous use of the front opening, one-piece back (i.e., no waistline seam in the back), and pleated fitting.

Over the course of the century, elite women used different skirt supports to create different silhouettes. A round hoop was very fashionable through the 1730s, but by the end of the decade, it was compressed into a flatter shape in the back and front; by the mid-1740s, a very flat shape was preferred, sometimes even with corners, but within a decade the more rounded shape of the late 1730s was back in style. Gradually the hoop fell out of fashion entirely, in favor of the soft bustle pad ...

Except in court dress. Around 1750, the mantua stopped being fashionable - instead, wealthy women wore sacques, gowns with flowing backs that floated over the fitted lining beneath. In the English court, however, a fitted gown was still required, and would continue to be until the end of the century. Hoops were also required for the court mantua, and later court dress, until George IV came to the throne in 1829 and was able to change the protocols. They also clung on a bit in very formal balls, but nowhere near as long.

So I'm not really sure what you mean by "mantua" here, or what you mean by saying they were only worn at weddings and very special occasions. But I think that at base, you're just asking how they managed their hooped petticoats.

There is not really a traditional "historical" answer to that question, as textual sources don't tell us. We do know that in the eighteenth century, control of one's body was very important, and as clothing is an extension of the body, it would also have been important for a lady to adequately control her hoops, preventing them from bumping knick-knacks off of tables and catching in doors. From experience, I can say that the average-sized hoops really wouldn't be that difficult to control - it quickly becomes second nature to turn your hips slightly to angle them when necessary. For the widest court hoops of the mid-century period, more work would be needed to learn to be graceful, which was really part of the point. More work would also be needed in terms of servants to open doors, assist, and get other people out of the way, which was another part of the point. (The expense of all that embroidered fabric and the display it could make its the third part of the point.) But ones that size were very rarely worn, and there was no specific etiquette to their use that we know of.