Have removed a number of decals for alot of different reasons. What has worked best for me is "OPPS" which in a sense is the same GOO-GONE and many other removers.
What I found to be the key is that I would use cotton balls which I would soak with the removal liquid. Rub gently making sure that you are saturating the tacky area. As the adhesive begins to break free, the cotton ball will load up rather quickly. Upon this happening, grab another clean cotton ball, soak it with the solution and begin the gently rubing process again. Allowing the solution to soften the adhesive is the key. If you do not let the solution do it's work, you will end up making a sticky mess and only become frustrated with your results.
Upon completion, make sure that you wash the area using some kind of rv/car wash detergent and warm water. When dry, apply a coat of good polish/wax of your choice to protect the surface and remove any ghost haze left on the clear/gel coat from the removed decal.
Good luck and remember to be patient.