iNate, I'm very much in the same boat as you. I think the hardest part is sticking to working out at least 3 times a week and trying to remember to constantly eat throughout the day.
The digestible proteins I've come across are: rice, pea, hemp (hard to find a tasty mixer) and unflavored whey. Perhaps drinking three protein drinks a day, in addition to regular meals, would be the most feasible digestion-wise way to gain weight? Other than that, I boil eggs (6g protein, easily digested) at the beginning of every week and eat a couple throughout the day, every day. Also eating good fats (avocado, e.v. coconut oil, olive oil and nuts...) seems like a good idea.
I recently read a theory that suggested nearly fasting oneself, all day until post workout immediately followed by super high protein/fat meal, stimulates natural human growth hormones and packs on more muscle. I guess some scientists are saying your body makes the most of the protein/fat if you purposely deprive yourself of proteins/fats all day until after workouts. Obviously, this wouldn't be a good thing to do everyday, and most althletes would probably tell you that constantly eating is the first priority; however, this fasting approach, in my opinion, makes some sense for one day out of the workout week.
Another tip, from mercola.com, I might incorporate for the last workout day of my week involves the "How to Perform Super-Slow Weightlifting" section of this link:
http://fitness.mercola.com/sites/fitness/archive/2012/01/06/dr-doug-mcguff-on-exercise.aspx
On the supplement front, I might add taking D-ribose a couple times a day, on workout days. This is SUPPOSED to keep up energy and stamina. Also, digestive enzymes might/might not help for us to assimilate fats/proteins into muscle.
Just before 2012 ticked over I started to break myself into the weight room, but I've managed to injure myself (New Years--nough said--and snowboarding) a couple times to delay my progress by nearly 3 weeks. I'll start again this week...
Hope this helps.
I'd like to hear others' thoughts on weight gaining...