Gwen Stefani, Blake Shelton -- Tight in Flight

Gwen Stefani and Blake Shelton are muzzling the doubters with this photo ... they jetted off Saturday, apparently for fun weekend.

A lot of people thought the whole thing was a ratings ploy for "The Voice," but sweeps and the season are over and they're still tight.

We're told Gavin Rossdale is taking care of the 3 kids while Gwen's gone.