It is common for the court to use a party's year-to-date income and/or W-2s to show the annual income of the party. This is very useful when a party has varying income during the year (like here). Both parties must bring income information to the court hearing (including paycheck stubs and tax returns). With information showing that the opposing party earns a good income annually and, you explain the issues to the court regarding his periods of unemployment due to his union position, it is plausible that the court will apply an average monthly income to the opposing party and you will leave your hearing with a support amount that you feel is fair.
DISCLAIMER: This answer and any information contained herein are intended for informational purposes only and should not be construed as legal advice. You should always seek competent counsel for advice on any legal matter.