The thing about weathering is, less is more, especially when it comes to rust.

Mud and dust build up and you may get subsequent rain streaks in those, but rust streaking in an operational Tiger most likely would'nt exist. These were prized possessions, more akin to a train locomotive than a relatively disposable T-34 or M4. They were incessantly maintained, even in the field.

You'll find surface rust on metal exposed metal areas like used spare track links, or exhausts that the paint and grease are burned off, in shell and bullet splashes over time, but painted areas, even high traffic like hatches are pretty resilient.

Look to the 1/35 static modelers for ideas on weathering, especially guys like Mig who have tons of tutorials out there. There are plenty of options to make a Tiger look ratty; worn whitewash, mud caking, exhaust burns, fuel/oil spills, over spray as units/campaigns change, etc.

Another thing to avoid is the black muzzle brake. The sole purpose of a Tiger was to transport that 88 around, it was cleaned and patched constantly, that's what the rods on the side are for. Besides the fact that the brake blew gases out horizontally, slowing recoil, why would the entire brake look like a charcoal briquet?