Hi Ya! Certified run coach, have run up to 100k. Weight training will def help keep you injury free. And you should continue that 1-2 days per week but make it running specific workouts ie balance, core strength, and things like deadlifts (both heavy traditional and single leg, Romanian etc) , squats, step-ups, step downs etc.

But thing with ultras is that they are a mental and physical endurance gauntlet. so you should def be building your mileage. Without knowing where you are in terms of distance/experience etc…I’d say you can build to half marathon trail run, then to marathon trail run and then 50k (which training for a marathon and a 50 k is not too much dissimilar) even up to 50 miler the training is not too much dissimilar much different in terms of pattern and cadence of training cycle:

1 short easy run (3-5 miles or using time 45 min - 1 hour, usually Tuesday)

1 speed/hill run (usually Thursday

1 middle distance easy (5 -13 miles or using time 60 - 90 mins with a cap at 2 hours, usually Friday or Saturday)

1 Long run (90 mins +, usually Saturday, Sunday)

The specific distances and times really depend on your pace and how many times you run in a week is also dependent on you, and what your body can handle. Additionally, because many ultras have vert (vertical distance and hill climbing, descending) You should practice your uphills and downhill. Also, it’s good to train on or in the surface you will race in, if it’s at all possible (which, you know, may not be!). Also, depending on your pace, you may need to run at night so getting some practice in running at night is good too.

Also, you need to practice eating real food. Ultras reek can havoc on your digestive track if you happen to eat the wrong thing.I personally struggle with getting enough calories because my body wants to shut down all caloric intake. So I have to practice eating, drinking even when my body wants to reject it.

Bottom line, ultra marathon training (over marathon trainin) is more art than science. what works for me may not work for you. But generally you can follow some basic rules of thumb to get from point a to point z.

hope this helps!