I don't know how "sealed" it is.
Traxxas sells sealed servos now. That would be your best choice for cheap sealed servos.
For the receiver and battery pack, drop them into a party balloon and ziptie the neck around the wires.
You can try to seal servos with balloons and/or plasti-dip and an o-ring under the servo horn, but I've always had water get in anyway.
I've had better luck using servos that are sold as "sealed". I use hitec 985MG servos for my throttle/brake servo since it's the one usually most likely to get water in it. Since it stands up, the water/snow collects on top of and around the output shaft. Then the water drains down through the servo and cooks it. The 985MG has o-rings on the case halves, case screws and inside on the output shaft. With a drop of RTV on the servo wires where they go in, it's pretty well sealed up.