This has probably been asked before, but can anyone suggest any other fics out there that run along the same lines as Ripe Wicked Plum's Castaway or Bloodshedbaby's Stranded? Thanks!

Try this one -- Not Your Ordinary Walk in the Park by Sandy After Buffy enlists Spike's help in fighting a strange demon, it sends them to another dimension. There, Buffy discovers to her distress that she must rely upon Spike for her very survival. And then things get really interesting.
http://www.bloodshedverse.com/stories.php?go=chapters&no=1572

Checking it out now! Thank you! All suggestions welcome and appreciated!!

Dreamweaver's Running Wild sort of, kind of fits, if you squint at it. Good story, anyhow.
http://spikeluver.com/SpuffyRealm/viewstory.php?sid=33038&ageconsent=ok&warning=5

I'll take a (narrow) look! Thanks!

Speaking of dreamweaver, His Way or His girl, sorry don't remember which one, Fits this rec.

It's His Girl

A wonderful fic that somewhat fits the bill is sweetprincipale's Offers You Can't Refuse:

Late S. 3 AU. Buffy's only way to stay alive and expose a plot by the corrupt Quentin Travers involves staying out of Sunnydale and staying one step ahead while Giles finds a way to save her life and get the evidence to stop the corrupt Head of the Council. But who watches the Slayer's back when she's the prey? If the motivation is right, Spike will do anything to help the woman he loves.

It's more of an "on the run in the wilderness" premise than a "stranded in the wilderness" story, but I think it's a great fic that should do the trick.

Another great one in the same vein is Eurydice's Promise of Frost:

Summary: When a snowstorm strands Buffy and Spike, they are forced to turn to each other for strength, especially when a missing Giles, mysterious visitors, and way too much magic threatens to turn it into a not so very merry Christmas.

Perfect! Thanks, you guys!!