try heating them with a hair dryer as you apply. If that doesn't work and it appears the adhesive is no good you might try reattaching with VHB tape. I've had those gutters on our
Uhaul for at least 4 years with no problems. I'm a great fan of Brake Clean so that's probably what I used to clean the surface. CAUTION: Brake Clean can damage some plastics and
paint. Or maybe start all over with new gutter