A yes, I know that feeling. Just now I managed to get my Moho transfer stage into orbit, with 300 deltaV to spare. Sounds like alot, but when I want the droptanks to stay on I can't rely on Mechjeb to calculate deltaV for me. So it was a frustrating mess of constandly almost getting it, than trying again, than throwing the 3th Kerbal out of the cockpit, than repeat the same thing. Over and over and over. Next on the list: 5 launches to refuel the damn thing. Than dock it to the lander. Than send up the engines.