Hi Victor, welcome to the DhO.
The issue sounds mainly to be one of consistency and momentum. If you're working mainly with the Mahasi model, consider the first three ñanas as being something like a ramp leading up to Knowledge of the Arising & Passing Away; 4th ñana can be thought of as a jumping-off point, a "peak" of sorts. You need to get some momentum going, although this comes
only through consistent and focused practice. I can assure you that it's possible, in fact recommended, to bring insight practice into your everyday experience and see the transient, empty nature of whatever arises in every situation. With enough intent and determination, it's possible to get the point where you're noting from the moment you wake up; to the point where you're mindful of whether your first breath upon waking is an inhalation or an exhalation.
If you have the opportunity to sit for extended periods, or to sit for several periods of no less than 30 minutes throughout the day then I strongly suggest you take advantage of it. Consider it retreat-lite and resolve to remain mindful during all of your activities through the course of your day; do mini-retreats, like 24 hours where you practice from 6am in one-hour sits and alternating between walking and formal sitting. There are lots of ways you could use your situation to engage in intensive practice which, if approached sensibly and with awareness of when to dial back if things get a little too much, would be conducive to landing Path if the intent is strong enough.
Less intensively, but with no less dedication: Concentration practice can be incorporated into a lifestyle where travel is common, as can noting and various other bare attention techniques. It's worth knowing that noting and bare attentiveness develop concentration, not in the same way as samatha does but to a level which facilitates a greater ability to deconstruct sensation. Use breath meditation while travelling, for example if you're on the train or bus then there's usually little else to do and these opportunities to practice are priceless. Some of the most profound and life-changing insights come from these moments, that paradoxical effortless effort involved in just observing with bare attention the way that experience occurs.
I've got a few suggestions on my blog, which sorely needs to be updated, that might be of use to you:
Methods of AwakeningWork on developing consistency in your practice and building that momentum, it is so, so, so worth the effort although it's not an easy process sometimes.
Hope this helps a bit, practice well!
T