Did you apply polish or wax before applying Future? If so, that's why it's beading up. You can remove the dried Future
with Windex or let it soak in a cup of Future overnight. Not sure if the decals will be affected.
I agree with Ted. I always use this method. I find the soaking time varies with the paint used.
As far as putty goes, I use Bondo and Purple Power never bothers it. I guess you'll have to
try it to find out.