For this circuit, why won't ".param thing" resolve?
You are trying to set a resistor value with a voltage that is only resolved when the simulation runs so this won't work. Instead, try calculating Vrser based on what the value of V1 is and, you can define the value of V1 in a statement. It then follows that Vrser is defined by a potential divider (R2 and the internal resistance of V1).

I have also tried &quot;.param thing={V(V1)}&quot;

V1 isn't a node on your circuit (it's the name of a voltage source) but, even if it was, you'd still have the same problem mentioned above.