hot water heater question.

Atwood water heaters do not use the Anode Rod. You might see if you can find a plastic threaded plug and replace the metal one if your heater does not use the rod. Good Luck and Happy Camping

A little plumbers silicone on the threads will help.

Anode rod used in Suburban Water heaters are there to protect the glass-lined steel tank from corrosion.

The anode rod is made up of drain plug with steel center rod and either aluminum or magnesium sacrificial material.
Aluminum ones will last longer BUT can collect deposits (calcium etc.) which can make removal of rod difficult.
Magnesium ones deteriorate faster BUT can interact with bacteria in some water supplies and cause a sulfur smell.

Routine draining/flushing of water heater helps remove build up in tank.

After removing drain plug, flush tank thru drain hole. You can purchase a 'wand' for this at most any RV Supply.
Clean up threads.......you can use a small wire brush (auto parts store) OR the best thing is to purchase a 3/4" NPT tap and run it thru threads.
Then use a small dab of 'never seize' on drain plug threads and reinsert into tank. This will help keep threads from corroding and make it easier to remove next time.

Replace anode rod when it has deteriorated 75%

The rod itself is suppose to protect your tank, so make sure you always use the plug with the rod. The calcium build up is something that will just happen, like rust build up also. The only solution I've found for my (rust) is to remove the plug often drain the water and then put the plug back in. Don't leave the plug out. If you don't keep the plug in, calcium and rust will build up on the threads where then plug screws in and then, yes, it's almost impossible to get the plug back in. Draining often (removing the plug) and then putting it back in right away will always break up any build up that may start. If you have lime build-up on the outside of the tank, the water is leaking through the threads. It might be time for a new adode rod (plug).