Option 1: Big-@ss Booster Build a big, single-stage booster under the payload. Add lots of fins at the bottom. Add radially attached SRBs, drop tanks, or asparagus-staged liquid boosters if necessary; make sure they don't interfere with the fins. Useful tip: Engines always draw from the most distant tank first. For vertical rockets, this means they empty the tanks in their stack from the top down, which causes the CoM to move downwards making the rocket less stable in the atmosphere. Solution: in the VAB, lock fuel flow from all the tanks except the bottom one. During launch, keep an eye on the fuel levels in the bottom tank, and, just before it runs out, unlock the next tank up. Alternately, just install TAC fuel balancer and tell it to balance fuel between all the tanks in the stage. Option 2: Traditional Vertically-Stacked Multi-Stage Booster (i.e. Saturn V-Style) The solution for stability is the same: fins at the bottom of the rocket. However, the vertical staging adds a complication: each time you ditch a stage, you have a new 'bottom of the rocket', which needs fins of it's own. But, since stock KSP doesn't have any deployable fins, fins at the bottom of your 3rd stage will be well above the CoM when you're burning the 1st stage, which makes them counter-productive. Thus you need to use successively larger sets of fins at each step, e.g. 2 small fins on your 3rd stage, 4 medium fins on the 2nd stage, and 6 large fins on the 1st stage. Unless you're trying for a purely ballistic launch, any stage that fires off above 40km or so can probably dispense with fins entirely, and just use reaction wheels or RCS. Option 3: Balanced Twin Boosters Instead of building one booster underneath the payload, use two boosters radially attached to the sides. Make sure the boosters extend up above the payload as much as they do below it, thus keeping the payload near the CoM. You'll still want a couple fins for control, but you don't have to compensate for payload drag just to maintain stability. This solution also lets you asparagus stage the payload's engines off the boosters and use them during the launch, thus boosting TWR. The downside, or course, is that your frontal cross-section is potentially up to tripped, increasing drag losses.