Good work, overall. Couple of points, though. Shermans often had huge piles of stowage on the rear deck, but these were generally M4's, which had a forward mounted intake cowling and a solid deck behind. However, the M4A3 had a huge intake grill for combustion air and cooling airflow, and blocking that grill would cause problems. Cooling isn't such a problem in winter, but it does looks like you've almost completely covered the grill. Also, snow build up isn't equal on all parts of a tank. As you've pointed out, firing the gun would dislodge or melt snow. But engine heat also prevents snow build-up on the engine deck unless the motor is shut down (wartime accounts often report that foot soldiers liked to ride on a tank's engine deck in winter, for the warmth).