I've had more success with 4RE opening into 2-3 fighting positions. It delays rifles, but it will help you quickly grab bigger portion of the map, because the kubel can't chase all the RE's around. build a quick forward fighting position and wait for the first engagement, RE inside the FP will hold out quite long so you can ninja cap around and you won't loose that much early.
I'm sure this is the best thing out there vs the kubel.
I was actually trying the exact same thing today in Semoisky. And there was some sort of bug where my REs wouldnt fire the riflenade out of the fighting position because I capped the point next to it with a Muni Point. Even though they could fire out and be fired upon.
Overall I couldnt pull it off because of this bug on that game and ended up getting hosed. Good to know I was on the right track.