Even in single digit temps you should be able to go a week between uses without any problems. If not, I'd start checking for draws with the ignition off, or load test the batteries. How's your charging system? Charge the batteries with a charger, turn the headlights on for a couple minutes to drain the surface charge, then read the batteries' resting voltage. It should be right around 12.6V, and your alternator output should be 1.5-2V above that. Don't forget to check amp output as well. Do you plug the block heater in? That alone should make for easy starting after a week. A couple hours before you need the truck is all you need. Get a couple battery warmers - I used ZeroStart 280-0063, $50ish each from Amazon - and wire them in parallel with your block heater. They're only 80W each so you'll still be able to run everything off a 15A outlet.