Start with Cherry Creek State Park.
H E R E - CCSP is a link to their camping page. Note, however, that it states a limit of 14 days within a 45 day period. They may have exceptions for winter camping. The Abilene loop is open all year and is reservable as well as walk in.
There's also Chatfield State Park,
H E R E - CSP is the link to their camping page. D Loop is open all year. There are FHU sites, but water is turned off between November and April. There is a dump station and potable water at the dump station during winter dates. Sites are reservable.
These two will be the best options in the immediate Denver area. Both are located in the south portion of the metro area; Cherry Creek is southeast, Chatfield is southwest. Both easy to get to.
There are commercial places to stay as well.
H E R E is the link to rvparkreviews. If it were me, I'd only consider the state parks, even if it meant moving from one to the other.
ETA: Just a sidebar, March is our snowiest month. But since you are from Rochester, you know a thing or two about snow :W