As far as I know epoxy primer is not a rust encapsulator. Rust encapsulators have chemicals that change the composition of the rust, making it inert, then seals it from moisture. Epoxy seals really well, but the rust is still there in its original state.
I don't recommend spraying or rolling epoxy over rust. Take the time to remove the rust.
You've got to have the capabilities and at least enough money to get some sand paper, a grinder with a wire wheel, and some rust converter? All it is is labor, and that is the most valuable thing you have in this hobby.
