It is important to keep your firearms clean and safe. Simple cases can be bought relatively inexpensively. If you have materials lying around and are not particular about looks, you can make your own and save money.
Obtain PVC pipe in the appropriate length and diameter to encase your gun. If you want to make cases for more than one gun, buy a long pipe and cut it down. Get end caps or plugs to fit the pipe you choose.
Cut the pipe so your gun fits the length with little extra space for the gun to shake around inside. Thread the ends of the pipe to match the end caps' threading. If the caps are not threaded, glue one on, and add a dowel to keep the other in place. Once you have put the parts together, if the gun shakes around inside, make a small pillow out of fill and cloth to stick in with the gun.
If you intend to store your gun long-term or under adverse conditions, use Teflon tape on the threads or otherwise seal the cap, grease the gun well and insert desiccant cartridges to absorb moisture. With this set-up, you can store your gun safely for decades. If you intend to travel with your case, check current FAA regulations for appropriate dimensions, and drill your case to accommodate locks.