They are somewhat pricey, but I can highly recommend a Jackery. It is a battery/inverter combo in a ruggedized shell. They come in various capacities, but 200W one is more than enough to run a Traeger. I use mine for long cooks to avoid any power glitches.
We detail solutions for powering portable pellet grills for tailgating and camping. We look at batteries, solar charging, and power needs for pellet grills.