"I like skinny guys"

What exactly is the problem here? Are you that unfamiliar with lifting that you think doing a high-impact strength training program is going to turn you into Dwayne Johnson overnight?

There is virtually no physical movement that is not augmented by strength training. A lot of strength gains are actually your central nervous system getting more efficient at coordinating your muscles. A lot of hard gainers - I'm one of them - typically say stuff like, "Yeah, I was a total gym rat during the summer. I didn't get huge but I got a lot stronger though." If you're already skinny, actually adding significant lean body mass requires you to consume more calories than you burn. It's literally physics - unless you eat at a caloric surplus, you won't gain mass. Where would that mass come from if you're burning those calories?

I don't think anyone on MRP advocates 'bulk and cut.' Most guys come into MRP as fatasses who were never below 20% body fat since puberty, which is why they describe their progress as "been lifting for three months, lost 40bs." A few come in as skinny fat, so lifting will get them some muscle definition and make them stop looking like an emaciated heroin addict with a pot belly.

But if you'd describe yourself as a "pretty fit" 150 lbs and 17% body fat, you can't tell me your wife wouldn't think you were sexier at 160 lbs and 11% body fat. That's roughly 20 lbs of lean muscle - and some fat loss - that makes you go from "Jon Hamm at the beach" to "Brad Pitt in Fight Club." Your net weight is only 10 lbs more, but you'll have a very different body, which will become readily apparent to everyone if you upgrade your wardrobe as well. Yet not so different that your wife or anyone else who prefers "lean guys" will be turned off. They will probably be very turned on.

Some women say "I don't like guys who look too ripped." And yeah, a bodybuilder who cut down to 6% on competition day, and has pictures taken in ideal lighting while flexing constantly and has those photo lighting enhanced in post-production - looks kind of ridiculous. But that same guy walking into a pool party would have every woman staring at him, he would look great but a lot more 'normal.'

Lean gaining 15 lbs of lean muscle will take you at least six months if you're 100% disciplined, closer to a year if you can only be disciplined about your diet/strength routine 80% of the time. If you think a couple protein shakes and reps on the bench press will turn you into JJ Watt, that's not really how it works.

I do a lot of outdoor activities too, and strength training only helps. Not only will your individual movements are stronger, and you'll probably find you're way less injury-prone and flexible. For the purposes of hiking/climbing or whatever forces you to lug around your own body, if you focus on strengthening your shoulders and lats, those strength gains will more than offset whatever mass you add. Which, like I said, probably won't be much until you start tracking your diet as well. If you're really that worried about it, hit the gym for a month but don't change your diet. I bet you'll notice some differences in your muscle definition when you look in the mirror, but your weight on the scale will be +/- 2 lbs from what it normally is.

TL;DR - Even you should lift, bro.