I inverted an offset dish for 30w. It is nowhere near being a birdbath. But I do have to bathe it, because birds landing on the feed support arms poop on the dish surface.
Outside of the multi-sat dishes for DISH and DIRECTV like the Winegard Trav'ler series, most all of the domes and in-motion systems use a similar configuration. The in-motion versions tend to use much larger dishes.Here is one for sale locally. It is a portable satellite dish that works with Bell & Direct TV. Asking US$100. Ad says it cost over $250 about 5 years ago.