It matters of course! If you wire those subs, with like 100ft of speaker wire, you are adding the resistace of all that wire, to your current resistance of the sub. extreme ex: 1ohm (wire) + 2ohm (sub) = 3ohm, the amp will see.
You can simply use a DMM: measure 1 end of the wire with 1 prob, and the other end with 1 prob. It will give you some type of resistance.
even 100 ft of decent speaker wire adds negligent amount of resistance. you would need thousands of feet of speaker wire to get anything significant. plus i see no reason for more than 10ft of speaker wire in the trunk of your car.
equation to find resistance of a wire with specific length and cross-sectional area: R = pL/A where p is the resistivity constant for the metal, L is the length of the piece and A is the cross-sectional area in m^2
for a 100 ft length of 20 gauge wire, resistivity of copper being 1.72 E-8 ohm-m, R=.79 ohm
since normal people use 16 or higher lets try 16 at what normal people would use in a car. 5 meters of 16 gauge wire gives .065 ohms or resistance. now if you are running high power you probably want to use something like 14 gauge wires and lets be more sensible and say we use about 2 meters of wire since amps are usually mounted right on the sub box. resistance is .016 ohms. there really is no need to worry about wire resistance unless you are stupid enough to use 100 ft of 20 gauge wire just to wire your sub.
lol when i answered him on this thread i was thinking the difference of length would be under 10 feet. unless you have a bus why would you need that much wire. lol.