My thought on this one, might as well ditch the ERSL (it's of little use on its own) and swap a PPC to the left arm, so you're not completely stripped when losing a single arm. Downgraded to a TC1 and added some DHS, losing some leg and head armor: More vulnerable on the legs, but it'll last a bit longer with those PPCs, and lets you poke out of cover on either side to get a shot off.
This won't work, timber with 2 ERPPCs is on the edge of being too hot, with 26 DHS, so you need similar amount. With 3 you will use the 3rd so few that you will actually lower your damage over the whole match, and you will even gimp the DPS of the pair having so few DHS. srm4 version
fx8230 is correct, 3 ERPPCs is too much for the Mad Dog to handle, there are simply not enough heat sinks.