Can my employer convert all stff to Exempt to cut out our overtime?

Hello,

I am an employee of a small Houston based oilfield company. I have read all about FSLA and still have questions.

My employer is switching all office staff over to Exempt from Non Exempt status. But here is my question...

Being as we are a small company we (the office staff) work large amounts of overtime and travel abroad to work on oil rigs all over the world.

By large amounts of overtime I mean very large. My personal earnings for 2011 were as follows:

Straight 40 hour pay - $45,000
Overtime pay - $29,000

While we are ok with going salary it appears that hour computed salary is going to be based Largely on straight 40 hour pay and eliminate the overtime pay that accounts for greater than %50 of our annual incomes.

Is this legal? How should the new salaries be calculated and to what extent must they consider our previous overtime pay when doing so?

Thank you so much.