First of all, sorry if any of this comes off as obvious, but I'm not sure how far you've been into Navarro yet.
*To the west of the gas station, hidden in the dead trees, is an access point for an underground ventilation shaft. The area around it is heavily trapped, so you'll probably want to dash ahead of your companions to reach it before they can damage themselves and/or have plenty of stims and a doc's bag or two ready to deal with damage and crippled legs. Following the shaft will eventually lead you to a locked door into the base, which you'll need a Blue Pass Key to open, and an intelligent Deathclaw. The Blue Pass Key can be found in the Gecko reactor building, and the deathclaw will agree to help you in the fight if you free him.
*Clearing out the underground area first makes things immensely easier, as it gives you access to elevators leading to various parts of the base, useful in hit-and-run tactics. It also provides you a safe, enemy-free area to take a breather and heal up your party, or to retreat to in a hurry if someone's on their last leg. There are no wide-open fields of fire or tough autoturrets to contend with, either, unlike on the ground level.
*The underground armory, once you fight your way there, has a few goodies that should make things considerably easier on you.
*Some people like to go this one alone so that they can snipe-and-scoot without having to worry about losing party members. If that's your style it may help to alternate between using the ventilation shaft entrance and the gas station trap door. If you do bring party members, it probably goes without saying that they shouldn't be equipped with anything less than the top-of-the-line-- gauss/caseless weaponry if you can afford it (or super sledges/mega power fists if you prefer close-quarters combat) and as many suits of T51-b or Combat Armor Mk. II as you can get your hands on. (Tesla might be sufficient, too, as I recall all of the base personnel being armed with laser or plasma weapons, but I'm not 100% on that.)
*If you want to finish the base off in one go, more power to you. If you're more interested in getting the plans with the minimum amount of effort/risk, the northernmost underground elevator will take you up to a shack at the rear of the complex. You'll have to deal with an autoturret and a few guards between there and the plans, but it's by far the safest route. Note that the plans are not in the hangar, as you'd expect, but in the big square building at the east side of the base, just south of the radar antenna. If you're lucky you should be able to grab them and dart back underground without any serious problems.