I think you need to run the numbers for the solar to decide. Either option is viable but the solar option is more cost and complication than just buying 300watts of panels.
- A generator is a throw it in the truck and crank it up when you need power (admittedly, an occasional oil change and filling the fuel) and that about it. You get as much power as the generator can provide for as long as you have gas.
- With solar, the panels are just the start and if you want to take advantage of them on the move, you need a permanent mount. You also need a charge controller mounted and wired in. If you want to run a high draw item like a toaster, you need a fairly large inverter. To power a fairly large inverter you need a decent size battery bank. This all comes with cost and complications.
I suspect by the time you are done the generator will be cheaper and more versitle. The biggest downside to solar is if you ever want to run the air/con, the solar is a no go.
Another alternative since you say it is being used for road trips is build the solar system but skip the solar panels. 6-8hrs with the truck hooked up and charging should be enough to top up the batteries negating the need for solar panels. You will still need the inverter and larger battery bank.