First disconnect the water line then take the bolts off that hold the toilet to the floor and lift up. Yes.
That leaves the seal still on the floor? Or on the bottom of the base.
What kind of sealant should I use to re-seal the toilet back to the floor? The seal is like a gasket made of a spongy material. Go to this link http://www.marksrv.com/sealandparts.htm it's part number 14. Reuse the seal if possible or get a new one at your local RV place.
I will have to do it every winter to avoid having to replace a $45 part every spring! If you can keep it from freezing you won't need to replace. RV anti-freeze or heat will do the trick.