In general the science supports strength training in reducing injury risk or small performance increases . I don't think there is any evidence it helps against cramping. Squats are good, especially 1 legged squats. General advice is you want a few reps of very heavy weights, such that you do 4-7 before exhaustion. Slow controlled lifts nothing explosive. Focus on muscles groups used in running. max 2-3 times a week on winter/low season, once a week in racing or high training periods.
That being said i dont ever strength train, partly because i focus on downhill running and get al ot of stress that way.
If you doing a trail race then 15 miles of trails will be more useful than 25 miles pf roads. Better put, it is better to spend 3 hours running trails than 3 hours on roads even of you cover a lot less distance. My total distance when ultra training is about 60% of my marathon distance despite running 30% longer per week.
Running on a flat road is obviously still good for general cardio but if your focus is trail races then i ould limit the road running 1-3 times per week. For m, in winter i do a bit more road running due to the dark, mud, snow etc it is often safer and in winter i am looking to maintain cardio mostly. This time of year a road run is a rarity when i am forced to due to travel or maybe if i have only a short time before work.
) wonder if theres anything i can do.