Nothing lasts forever in this world so rust will catch up to anything you buy made from metal. Some things are just made better than others and for that reason will last longer in the same harsh environment. If you buy something inexpensive and it lasts a long time then count yourself fortunate for getting an exception to the rule. My last gas grill was a bargain unit from Walmart. Uniflame is the brand on it. The thing lasted 12 years in the blazing heat of Riverside California. It cost me something like $150 and I never changed the burners. I am certain that I was the exception to the rule on that one. Care and environment play a big role. If you are near the ocean the salt air will definitely have an effect. Harsh winters can take a toll as well if your grill is just out in the weather.
My reason for suggesting the gravity fed from
Masterbuilt is that it has the set it to a certain temp feature. Which I am guessing is why you were interested in the pellet grill from your original post. But there is no auger to maintain and my guess is that there would be less overall maintenance. I know that vacuuming out a pellet grill is not high on my list of desired activities. Other than the fan there just seems like less moving parts to worry about with the gravity fed charcoal grills. Plus, you are still cooking with a wood source in charcoal or solid wood form. If I were in the market for a new grill or smoker right now that would be my choice for an all around unit. I still prefer the offset for smoking but that is just my personal opinion. I'm definitely interested to see what you finally go with in the end. Like everyone else here I am also anticipating some excellent Q view when it is all said and done.
G