speaker load

Yes, it will be a problem.  Not for the speakers, but for the head unit.  You cannot put a lower impedance load on an amplifier than it is capable of withstanding.  Look at the head unit specs and see if it gives a power rating at 2 ohms, such as XX watts @ 2 ohms @ 1000 Hz.  If it does, it is capable of driving a 2 ohm load.  But if it doesn't, it probably isn't capable. Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.