On Sat, 04 Jun 2005 06:56:41 -0700, Grant Erwin
wrote:

...., and use
2x6" tongue-and-groove fir for the deck.

I can't offer much wisdom with respect to the frame but I'd suggest
not using tongue and groove for the deck. Moisture and dirt get
trapped in the joints and you get a rotted out bed in no time flat.
Better to use just plain 2x6 and a wood preservative for some degree
of longevity. If you intend on hauling dirt, sand or gravel, stuff
that might fall through the cracks (I'd also suggest spacing the deck
boards about 1/4" apart for drainage), invest in some sacrificial OSB
to cover the deck whilst hauling the loose stuff.