Does dihedral improve roll stability in gusty conditions?
Dihedral does not help roll stability to a side force gust.  Quite contrary, a gust will roll the plane into a slip, which then will turn the plane downwind (courtesy of your elevator turned rudder).
Firstly, I would not recommend setting a model plane with excessive &quot;static stability&quot; in windy conditions.  You want to be staticly stable, but not so much that a gust will pitch you up into a stall.  Higher wing loading also helps.
But roll stability from dihedral is good for cruising flight, but no match for a side gust, especially in a model.
What you must do to keep dihedral is to put side area below the CG.  This is known as &quot;anhedralling&quot;.  Sea gulls lower their wingtips.  Cessna put the wing (and fuel) on top.  Consolidated built their famous PBY 3 Catalina with the engines on top too!  All 3 want to roll into the wind, not away.  This is the key.
A fourth design, the common paper airplane, does this with gusto.  The side &quot;keel&quot; balancing with the upraised wing around the center of gravity is best for cross wind roll stability.
So you may experiment by raising of lowering your CG, adding side area, and glide testing in a cross wind.  Your second model seems to have more of a chance.  You may try a shorter and more square vertical stabilizer, and a bit of weight (a coin or two) on top of the wing at the expected Center of Pressure.