How do I keep my vintage Fender amp in good condition?

Keep it dry and play it regularly. Rust comes from moisture — store the amp off the floor, use a dehumidifier or silica gel, and use a breathable cloth cover, not plastic. Tube issues come from cold starts and long idle periods — play the amp at least 20 minutes weekly, warm it in standby for 30 seconds before playing, and never move it when tubes are hot. Clean rust on metal surfaces with WD-40 on a cloth and tube pins with a pencil eraser.