All of that excessive cardio will play a role in decreasing your maximal ability to gain weight. As others will tell you over and over again, you have to eat a whole hell of a lot. Follow Berardi's Massive eating principles (it sounds like you have already read it) to keep from gaining too much fat mass while gaining weight. A good way to add calories is natural peanut butter. Put it in protein shakes or just eat it with you protein/fat meals. 1 tsp is 200 calories.
Stick to a program that offers a high volume to induce muscle growth but make sure that your reps per set stay in the 3-6 range. anything over that will greatly tax your body with the other intense workouts you do (hiking, MTB biking, etc.) It is important to not go to failure on each set so that your Central Nervous System (CNS) stays charged. I am currently loving Chad Waterbury's Anti-Bodybuilding Hypertrophy program and I think this would be great for you as it lets you get the benefit of high volume training but keeps your gym sessions short.
I would also look into a good protein powder (Grow!, duh) because it will be hard to eat all food meals given your busy lifestyle and Power Drive to make sure your CNS stays in optimal condition.
Eat like your life depended on it
Follow a high-volume program that wont tax your CNS too much
Get enough rest
Good luck and keep us updated