I do the same, with the emphasis on alfalfa hay. I feed smaller quantities of grain than does Trinityoaks and I add variety in winter with greens I dry during the summer months. The large mesh bags that onions and oranges come in are ideal for this.
I also feed some fresh foods in winter. Pumpkin, carrots, beets, squash trimmings and pulp (when we are eating it) and cabbage, which is cheap and keeps well. The thing about cabbage is that it is gassy and must be introduced very gradually. Not all rabbits can handle it from what I read, but mine have adapted to it very well. My rabbits also enjoy the occasional piece of baked potato. I've got into the habit of cooking an extra one or two when we are having them.
You can also grow grain grass in plastic dishpans indoors. It's very easy and excellent for the rabbits. Sprouting grains and seeds is another way to add variety in winter. A sweet potato growing on the windowsill will give more nutritious fresh foods.
In winter, the amount of fresh food is small... treat portions a lot of the time. In early spring, as the weeds and leaves come back, there is a natural increase in the fresh foods until by May they are getting mainly greens.
It is very important that the rabbits have a trace mineral salt block if they are not getting pellets. I buy the reddish brown ones about the size of a brick at the feed store. They are intended for general livestock and only cost a couple of dollar. I knock chunks off them with a hammer and put them in a small crock or ramekin in the pens.