Windshield washer fluid works good for non potable tanks and drain traps too.
To the OP, fwiw, it will be easier and cheaper to figure out how to properly winterize than to stuff everything full of antifreeze.
Idk how your camper is setup but you can bypass and drain the water heater, drain the fresh water tank and lines. Switch the water over to city water supply and blow the lines out.
The only antifreeze you really need is some in the gray/black tanks and P traps.
Couple gallons there and if you really want to, after draining and blowing out the water lines, run some into them if you fear that you didn't get the water all out.