Those are not solutions for a new camper. Those are workarounds for an insufficient system.
No you won’t drain the truck batteries during a meal stop. But even with 2 gc batteries or 2 typical 12v marine batteries, they’re only going to run the fridge and fridge only for less than 12 hours in the heat of summer. Less if one is actually actively using the fridge. IE opening it frequently.
And even less with one cheapo battery like the OP has.
How this is even a remotely workable solution for anyone short of those with very robust aftermarket 12v power systems is a mystery.
It literally defeats the purpose of one of the main luxuries of having a camper vs traveling with coolers and ice.
Basically the OP and everyone else in this situation have been screwed into an inferior product/situation. No matter how much the Defenders of the Compressor Camper Fridge Society try to downplay it.
Of course buyer beware applies here and it appears this buyer like any others have no knowledge nor did they seek any before becoming RVers. But to their credit, who’d think you’d get a basically unusable system in a new RV?