I think some of the plants which appear in the "alpine" section in garden centres can be aggressive and take over a whole trough. You should be ok with saxifrage. Sedums and houseleeks tend to spread about quite a bit. Troughs dry out fairly quickly in hot weather so make sure you water them well, perhaps before it gets hot in the morning and again after it has cooled down in the early evening. Make sure the troughs have plenty of drainage to prevent stagnant conditions, a sure way to bring an end to alpines. It is also good to visit an alpine plant nursery and talk to the grower who will advise on suitable plants for troughs and their needs. Good growing. We are all still learning about plants, even though we have been growing (or trying) for many years.
