Can I winterize my Pop-up camper myself?

I agree with Skyline Nomad about not putting antifreeze in the tank. It is near impossible to get it all out when you open up again and even if non-toxic you will not be happy with the pervasive smell in your drinking water. Empty the tank fully. Push antifreeze into the pump and lines between the pump and faucets including any shower faucets OR push air through with a compressor and leave valves open to dry.
Its not as hard as it might sound.
Other hints: moisture from condensation is an issue in a unit closed up for long periods. Close up following the driest weather you can. Empty the unit especially of anything cloth. Open fridge door or take it off. Spray down with Lysol disinfectant liberally on all interior canvas and cushions. (Don't worry the smell will dissipate over the winter). Remove batteries including those in the smoke detector and leave off the cover so you remember to put them back in. Stack in a half dozen of those chem-dry containers. Add a few mouse traps or bait. Put these last two items in an accessible place so that you can check them from time to time.
When I open up in the Spring the unit is clean, free of vermin poop or damage and mold free. Ready for camping fun.