I am using a cheap one from last year's Tampa RV show. You don't need it until you do! I've seen some really stupid things from my RV driver's seat over the years.
You'll have to get it online, they are cheap enough that if the first one goes bad, you toss it and get another. Mine uses a memory card that you buy separate. Make sure it ships from the US, or you will be waiting for the slow boat from China!
Only some of us learn by other people's mistakes, the rest have to be the other people!