So after many many many ( lots more many's ) tries I finally got my SPG-15 completed for the Stug IV, and I also managed to complete HT-15 primary and secondary conditions in my 4502A of all tanks ( blocked just over 3.6k dmg, dealt just over 2.5k dmg ). I ended up loading up 10 HEAT shells in my M44 SPG and let loose, did just over 2.6k dmg, was 3rd in xp, top in dmg but we still lost the match. AND I DON'T FREAKING CARE cause I completed my mission.
Now the grind for the 4502B begins in earnest seeing as I'll be transferring my Sisterhood of Steel crew to it once I've purchased it, but I won't be able to transfer them to the Maus after that as I'll need an extra crew member.
Disregard the 2nd half of that previous sentence, I just worked out once I completed the HTC set of missions I'll be able to have a full SoS crew in the Maus as well.