I've never seen the Outpost full, so you should be fine.
A tip if you need to park at the Settlement - the lot across from Trail's End is hardly ever full, even at dinner time, so you could always park there and walk down to the beach/boat. Or if you're really stuck, there is a large parking lot across from the bus stop at Settlement. I've only ever seen golf carts there, but I've always wondered if you could get away with parking a car there to pick up a nice Giddy Up and Go from Trail's to Go lol.
Always plug in the cart before you go to bed and you should be fine all day. And if you've never been there before, you'll see that all carts look alike, so try to bring something to tie onto your cart to distinguish it. A bit of garland, some flowers, some gel clings, that you can pick out in a crowd.