I'm an ectomorph/hardgainer etc. trying to gain some mass/muscle.
In other words, I'm 31 years old, fairly strict Paleo since the last 2 years (except for optimizing my omega 3 profile), 5'9" and 143 lb. I'm almost back to my 145 lb pre-Paleo weight, with a significantly improved body composition. I've been doing barbell training and martial arts for the past couple years, but realized I need to take it up a notch, so I started Crossfit recently to improve my technique as well as consistency (still in Fundamentals, haven't started regular class yet).
All the research I've done on Paleohacks/Whole9/Lean Gains etc seems to indicate that I need to significantly increase the amount I eat (and add sweet potatos etc), especially on workout days. Here's my question: if it works, and I pack on another 10-15 lb of muscle, do I need to keep eating like crazy even to maintain the acquired mass gains? I simply don't see heavier buddies eating all the time, so I'm wondering if its just temporary until the mass has been gained, after which I might be able to stabilize at a level where I'm eating more than now, but not the 1 gm protein/ day, 4000 cal/ day level in perpetuity.
Does that also imply that rather than not eating enough I have a gut issue? I did have IBS which was mostly cured by Paleo but flares up mildly from time to time and is not quite eliminated yet. Is IBS/stomach trouble common for hardgainers too, and the real reason for inability to gain mass easily?
The advice to eat more to gain weight is based on the assumption that you need to be in a caloric surplus to gain mass. For the most part this is true, although it is possible to gain weight without being in a surplus as long as your meal timing is in line. However, once you want to maintain weight, you don't need to be eating in a surplus. Having said that, since you will have more muscle, the amount of calories you eat to maintain weight will be more than it is now.
Realistically, if your goal is to put on muscle, and you are doing crossfit, you can't eat too much.. particularly on workout days. Eat your biggest meals around workouts, and you will be fine.
As for gut issues, adding some probiotics might help. Also colostrum supplements (if you do well with dairy) and l-glutamine may help. The fact that IBS is better with paleo and flares up from time to time makes me think that it may be gluten that causes problems. Be careful of gluten when you go out to eat as that may be a cause. Flour is used as a thickener in many sauces and dressings where you wouldn't think of it.
Once you reach your goal, you ought to be able to relax on eating. The key issue of whether or not you keep the muscle is whether or not you use it. As long as you are exercising enough for the body to think it is a good idea to keep the muscle around, you will likely have enough of an appetite to just eat until you are satisfied in order to maintain the muscle.
Strictly from experience here, I have eat TONS of food to escape my skinny awkward frame for my entire life, and never accomplished it. Now I'm only eating when I'm hungry, I'm still skinny, but just look less awkward. For chronic skinny people like us, force eating doesn't work, I've been trying it for 10 years, and probably what destroyed my gut and have me depression.