If you have the Thetford Aqua-Magic Style II round toilet like I do and you're not happy with the seat, read on. The cheap thin plastic seat that Thetford supplies is terrible. It is flimsy and hard to clean. It is a dull plastic color, not the shiny seat like you have at home. The hinge on mine was broken (but still usable) so I went on a mission to find one that fits. If you just go to the big box store and buy the any 'ol round seat they have you will find 2 problems. The seat is too short so it doesn't come to the front of the bowl. The back of the bowl is exposed when the lid is closed. The seat I finally found is the American Standard Fluent Round Front Toilet Seat. It's a little hard to find - I suspect they don't make it anymore. The fit is just about perfect and the price is cheap. I bought it at menards.com for under $15 plus shipping.
ETA: I added images but not sure why they are not showing up. Here are a couple links: