Here are the two I've used before with success (with your same code!).
Coupon code MUGZ029 - $30 off
Coupon code MUWZ023 - $25 off
*Please note that that is a zero in each code, not a capital O (I made this mistake before)
Please note that if your coupon code is accepted, the deduction won't show up on you confirmed price. The amount will be deducted at the end when you return the vehicle. Also, you do not need to produce any type of physical coupon to use these coupon codes.
I am not sure when these codes expire. Hopefully, they will work for your dates.