One of the better marine facilities in the Denver area is Calibre.
I was once told by a trusted friend years ago that if you wanted good body work done on an RV, go to a place that works on boats as they are really familiar with fiberglass and gel coat repair. Not sure about the accuracy of that statement as I've never had a boat and neither have I needed extensive body repair on any of the RVs we've had. But it does make sense and I've heard it from several others after that through the years too.
Calibre Marine Body Shop & Paint ...RV page go HERE
5505 East 48th Avenue
Commerce City, Colorado
I do have in my notes that there is another marine and RV body shop in Littleton but there's only one entry I made in my journal of somebody saying that they had body work done there but thought it was just an average experience and nothing special about the work or the service.
Marin's (RV page)
But nothing extraordinary like Calibre has the reputation of being ...Calbre is highly recommended.
I'm sure others will have suggestions too as the Denver area has a lot of good general collision repair and body shops.