If you live in a humid environment and don't use it for 4 months I suggest whats already been said to remove the safety grate, vacuum out all the pellets, then run the auger in test mode, then vacuum all the pellets out of the firepot. IMO all a cover does is trap moisture under it and hold it...
Why would you want to make a mess near impossible to clean up? the drip pan also spreads the heat as evenly as possible. Line the barrel with foil to catch the mess.
My opinion is to remove the saftey grate. It's nothing but a CYA for RT in case some fool or a kid gets gets their finger in the auger. Tho as slow as it turns I don't see how that's possible. I think it would take a lot of stupid to do it.
It can vary depending on brand and type of pellets since make more ash than others. When the firepot ash builds up deep enough then igniting pellets becomes a problem.