You have several choices in cases. A soft case may be fine for short trips in the truck, so long as it’s on the back seat and not on the floor, the bed or the trunk. If you’re traveling any great distance or on rough roads, a hard case becomes a much better option. Even a thickly padded soft case may not protect your favorite deer rifle should you drop it, or drop something heavy on it. And bumps and rattles can easily jar your scope, rendering even the most expensive optics worse than useless.
When traveling off-road on an ATV you should consider a hard case mandatory. Yamaha offers hard cases and several mounting options for both four-wheelers and Side-by-Sides. They’re padded on the inside and mount securely to the frame. Still, you should always ride gently when transporting cased firearms.
For air travel you have no choice. Your gun must be in a hard case capable of being locked, preferably with TSA-approved locks. TSA has keys for most lockable gun cases, and many newer cases are marked with a TSA lock number. Unless advised otherwise, bring it to the airport locked. Unlock it for inspection. Then lock it back up when instructed.
If possible, try not to case your gun when it’s wet. That will only introduce moisture to the inside of your case. Dry it off first. If you do get the inside wet, dry it out before you use it again. Don’t leave your gun cased for extended periods. Trace amounts of moisture may remain trapped and can also lead to rust over time. You can alleviate some of this by inserting the gun into a moisture retardant gun sock before casing it. And last, but by no means least, never transport a loaded gun in any motorized vehicle.