You're making good progress here, not bothering with correcting everything Trumpeter has wrong, like the 1:35 scale gas pedal or the mounting bolts for the periscope glass holders going through the actual glass... Looks like they haven't bothered correcting anything they did wrong with the Tiger II kit. The lower hull warping bring back memories...
The tank on the firewall you ask about, is indeed a fire extinguisher, and it should be painted red.
Curious about the shiny part of the shock absorbers. It should be all primer red.
This is one as seen in the Tiger II they're currently restoring in Thun, Switzerland:
Good luck on the rest of your build!
Arild
