Not much you can do except cover the tray with foil and keep the grill relatively clean. Every time you cook you'll sterilise the grill interior. Even stainless will discolour and rust. I make sure the grease trough on my 650 is wiped out and I run a piece of paper towel through the channel to the drip can.
The older grills have a slightly different grease pan but the same procedures apply. If your tray warps or pits through request a replacement. There's a 3 year warranty on them. Out of warranty they're $10 shipped.
Traeger sell a foil cover for too much money. I can cover either the original design or the Ironwood with the standard width foil in about 5 minutes.