Technical transport laws, and I should know by now...
Real guns; trigger lock or similar device. If trigger cant be locked, disassembly is an option. Guns are then placed in a locked container (nobody specifies if it has to be hard or soft, just locked), and put in the trunk of the car. If a trunk is not available, under cover in the hatchback is fine.
Airsoft? There are no transport rules. None.
However, it's common sense to at least remove the mags (if there are any) and cart the guns around in a locked container or something discrete that does not scream 'gun' to any onlooker. Trigger locks are not mandatory. A locked case is not mandatory either, but a darned smart idea in general.
Police searches? That depends on what they are looking for and how they ask. If they do intend to search, please tell them there is an airsoft gun (fake) in the case, vaguely what kind/type, and be awfully polite. They may not have a legal right to cuff you and take you away, but you'll have to argue that from jail.