I'm not sure the Rhino lining is any good on top of rust. It probably would be if the rust surface were prepared first. But something you could do yourself that would be almost as tough, and also stops rust, is POR-15 treatment. If you're not familiar with that product, a search here on the forum will turn up some hits.
Also, I would warn you that if you have water coming inside the car and settling under the carpets, you are in significant danger of having the floorboards rust out from under you. By the time you get obvious warning signs, like a soft spot in the floor, it will be too late. At that point your floor is being held in only by the undercoating.
If it were my car, I would have the carpets out of there and would start getting up the water-absorbant black foam padding that is glued to the metal floor. That stuff holds water forever against the metal and eventually it rusts. Get that stuff up, remove any loose rust chips (I hope you don't have significant rust) and give it a POR-15 treatment. That stuff dries to become really hard. Then you can find some kind of carpet padding that is more easy to remove as a substitute.
The same thing applies to the area around the jack mount holes. It starts to rust in one little spot and then spreads underneath the undercoating. POR-15 will stop this kind of rust too.
I may be conducting a project this summer to remove all the undercoating from my 240D due to it no longer holding a seal against moisture - at that point it absorbs and retains moisture.
Ken300D