The second one (the passage) is freestanding (meaning you don`t necessarily have to stake it down, as long as you can keep it from blowing away with stuff in it - and looks like it has a pretty reasonable sized vestibule - i.e. likely enough for some gear and or a wet or dirty dog when they get that way - just in case you *don`t* want to snuggle when pooch gets that way.

$129 is a pretty decent price for such a thing, and REI is not a no-name thing - their in store stuff is usually pretty solid, and they will normally stant behind it if there is a problem.

It`s heavier than I`d want for lightweight backpacking - at a bit over 3.5 lbs - but it`s not bad, and if weight is not your primary concern it would probably serve you well.