It's almost impossible to find a sample memoir proposal. I spend hours and hours trying to find one on and off line.
I just started querying this week and I've been told that memoir submissions are the same as fiction submissions. So far no one of the agents I've queried wants proposals, but mine is ready to go if they want it. So far 1 agent wanted a partial. I'm definitely glad I have mine done, it took me longer than the first draft of my memoir. LOL. I ended up doing about 6 drafts of the proposal and 10 of my memoir (but I might tweak my memoir again if I don't get any solid bites from the first round of queries).
I wish I could be more help.