How would I be able to install trusses on the building walls in which the tails were pre-cut to length, and have them come out perfectly straight to one another, without using a string line, mainly because of wind?
I've rarely used a dryline to set trusses. Plumb and straighten your walls, then set each truss heel to the same wall. Be sure to not rotate truss direction from one to another. Because the truss plant's jig probably isn't perfectly symmetrical, this would result in humps in the roof plane.
If you can't straighten the walls, chalk a line on the top plate from which to set heel position. If wind is a factor, use an eye from one end and have an assistant (or two) pin the line in position at midpoints and snap each way.
How do you make sure you have a perfect rectangle - corner to corner will always be equal - make your measurement the third angle of a triangle.
So for all intents and purposes your question asks how to do this with out a string line and your concern is because of the wind.
A perfect rectangle will have equal length from one corner to corner measurement (South-East to North-West) as it will from the other corner to corner (South-West to North-East ). Because basically it is two right triangles joined together.
So if you start at placement with your first truss - you make one measure on one side after that it is simple. See my example picture - black lines are trusses , orange lines are wall supports and the light blue is a measurement you make - whether you want to use a single pre-measured string or tape measure - you are not doing this by dragging a line across the roof .. and this is easy enough with a laser line as well (maybe easier).
You can place the first truss and measure where to put the second truss and cut a line at that point - or use the Pythagorean Equation A² + B² = C².
A² = Truss length. B² = center on center truss to truss. C² = my little blue lines distance corner to corner.
A laser will work fine and you will not have any huge setup time - this is easier than you think.
[If the math is too much use the scientific calculator on your computer.]