I used to have this problem and got to the point I was using 600 grit to prep the body. I then found duplicolour clear plastic primer (tamiya safe, not sure about other brands) and find a couple of light coats of it, left to get tacky then given normal primer seemed to work for me. Also when removing the tape I warm it slightly with a hairdryer to soften the glue, and pull it back along, almost bent flat back over itself (almost flat back) rather than away from the body so theres only tension between the tape and paint at the end. If you pull it away at 90 degrees it will put more strain on the paints adhesion. think of it like pulling on something thats been clingfilmed, if you pull it the whole lot moves and this is similar to what happens when pulling tape at too steep an angle.