Rick wrote:
How do I calculate the voltage rating I'll need for capacitors used to
make traps?

I am making a portable field antenna for 160 through 40 meters, for use
with 100 watts absolute maximum (normal use will be from 5 to 50 watts).

I don't know of any general way to calculate it, but you can easily get
the data from a model. In EZNEC, clicking Load Dat will show you the
voltage across and current through a "load" (in this case, trap), as
well as its power loss. Other programs have an equivalent feature.

Roy Lewallen, W7EL