Many have already suggested: make the crew RA from 1 to 1.25. This will make them have the same effective HP to small arms damage as the 4 man crews of other at gun crews but still be just as resistant to explosive damage which was what the rak crew struggled with when they only had 4 men.
+1
Agree with this or at least 1.15 or something. I don't want to remove retreat because it's cool and unique, and it was just too squishy before at 4 man. But 5 man + retreat is too much, it's too easy to A-move overextend to get shots off and then run away (especially with double rak this can punish Mediums super hard).