We have a full-size pickup truck that is primarily used to take our trash an recycling every 3 weeks or so. We use it when we need to haul larger items, but that’s a once-in-a-while thing. It’ll also be driven when one of the main cars is in the shop for service. But in general, it sits except for the trash runs - about 13 miles round trip.
I’ve seen conflicting info on line - saying it should be driven weekly, monthly, just idled for 10 minutes a week… Is there a problem with it sitting 3 weeks or more without being moved? If it matters, it’s a basic truck - no fancy power accessories - it even has manual windows and locks. Automotive experts, please check in. Thanks!
I disconnect the battery on my RV and it sits for several months without running. I’ve seen no ill effect from this. I would suggest adding a gas treatment to your truck’s fuel tank, as it’s not good for gasoline to sit for long periods. Otherwise, I don’t see any real problem with this.
weekly would be good.
depends on your environment for actual effects. rust, corrosion, grime can build up on parts if left to sit. tires have problems with the weight and no moved.
I think you are OK. You have proven that it works. The parasitic drains on the battery have not been enough to prevent you from starting. A 13 mile run is decent enough to get it warmed up and charge the battery. Don’t try to live with that battery forever. About four years is when I change them, but I keep checking from time to time with a load.
When it sits that long all the oil has run off certain parts. Wear is greatest when you first start. That can’t be prevented. I used a little STP for the hell of it. With that usage, wear is not going to get you anyway. The fuel may run back to the tank if the check valve is not holding. I prefer not to grind my starter. When I let my truck sit more than a week I will “key on” the fuel pump one time or two before hitting the starter. This pressurizes the fuel system and it starts with a flick of the key.
You do run a slightly greater risk of tire rim leaks in my opinion. And if you can be parked off the dirt or grass, that will reduce the undercarriage rusting. Keep the fuel tank reasonably full to prevent condensation. They say that modern systems don’t have that problem, but I still observe this old time preventive technique.
I hadn’t thought about a fuel treatment, but that’s a good idea. And I do try to keep it full - generally when it gets to about half a tank, I top it off.
Unfortunately, the spot where we have to park it is dirt, but we plan to put down gravel - this spring, I hope. We were also talking about buying or building one of those one-vehicle carports to protect it from sun and sap and bird poo. We’re hoping we’ll never have to replace it, being old as we are. 
I figure it should go in for servicing every 6 months - or is that too often? I can’t imagine we’d manage to put 500 miles on it in that time.