Proving hidden income

My ex-husband has been and continues to earn "cash under the table" income. He refuses to pay more than $109.86 every 2 weeks. He has a school custodian job to prove that he is earning legal income but I know for a fact that he is also earning way beyond what he claims to be earning. If he is caught, that would be income tax evasion, perjury to the court and back child support. He refuses to put my son under a health insurance plan to pay for his portion of my son's health insurance. But, he has a boat, has purchased 4 vehicles since our divorce in 1995, just purchased a motorcycle, is able to go on various vacations, etc. This does not account for the amount of money he is making even though he claims he is only paying $300-$400 for the condo that his live-in fiancee's sister owns. I haven't done anything to avoid hurting my 9-year-old son. But this situation has caused me to file Chapter 13 (since he didn't work during the time of the divorce, I ended up keeping most of the bills including the house). Now he will be getting married. Here are my questions:
1 When he gets married, how will this affect my child support?
2 How can I prove that he works elsewhere and is getting paid "cash under the table?"
3 Are there any services that is able to assist me?

Answer to #1 is that child support is still due. He may try to seek modification due to his new family, but I don't know what chance he would have.

Is the support court ordered? And is he behind? If so, contact your local DA's office of child support. They would be able to go after him and possibly find out his true income

Have you contacted legal aid or your local bar association for a list of volunteer attorneys?