I think 120kWh is the minimum for a "grocery getter" or "Home Depot runner" because then it should have around 250 mile highway range. And I think this will be the base battery size.
If someone wants to tow around their camper though, I think that a 250kWh pack will be required since consumption will be around 1,000Wh/mile while towing. The unladen range (non-towing) range of this version will likely be over 500 highway miles.
A 250kWh pack will be able to take full advantage of 150kW Superchargers nearly all the way to 90% SOC, but you're still looking at nearly 30-45 minute stops if you are towing and trying to hop between chargers.
Long story short, I think Tesla is capable of making a usable EV truck, but hauling the travel trailer across the country will still require extended charge stops. Hopefully those who enjoy camping learn to enjoy charging stops.