Power optimization for high-side switch
I recently received 4 of these :-) !!!
I haven't tried them yet.
IPB180P04P4L-02  :-)   :-)   :-)   :-)
IPB180P04P4L-02 datasheet here
P Channel MOSFET, 40V, 180A,
1.8 milliOhm typical at 100A (!) with Vgs = 10V at 25 C.
2.4 milliOhm max same conditions.
At Vgs = -10V Rdson is about ruler straight through 180- Amps.
It will be higher at higher temperatures.
Pricing here $6.38/1 at E14 / Farnell and less in volume
$2.75/1 Mouser - 6000 in stock.
$1.31/1 Avnet !!!, - no stock.



Drive  resistors are non critical for occasional on/off.
With 1K you'll get maybe 10's of  uS switch time worst case but minimal loss overall. 

BUT Vgs_max matters. For the IPB180P04P4L-02 it's 16V max, so a 10V clamp (zener) woul;d be in order if using more than 10V drive. (You usually get to exceed Vgsmax only once per MOSFET lifetime. 

Check data sheet for your FETs.



Your loss calculation has gang aglae.  


  4.2 mOhms for Vgs = 10 V ... If my calculation is right, the power loss would be about 0.25 W for a load of 60 Amps.


Power = I^2 x R = 3600 x 0.0042 =~ 15 Watts.

For the IPB180P04P4L-02 at 60A at say 2 mR that's ~= 7 Watts.
My package is the TO263-7-3.
3 n+ 1 cut off + 1 in TO263 pkg with bent pins for SMD.
Tjc = 1 K/W = 7 K rise at 7 Watts.
You want some sort of semi real heatsink  for this at say 10 Watts to be safe.
At 5 C/W (easily enough achieved that's about 60C rise for 10W.
Lower C/W heatsink = cooler.