I've done a number of waterslides - the 43rd's are mostly exclusively waterslide tyre decals. But don't take this as gospel, it worked for me - thusfar!
Firstly, you get rid of the mold lines (obviously). Then add a sealing layer. And yes, as said above, NOT enamels. I mostly use acrylics and once even tried floor polish to good effect (the Future-ish stuff - we don't have "real" Future here).
Apply decal as normal. I also use Tameo extra strong solvent on their decals. (But that is SERIOUSLY aggressive, be very careful if you do use it!) Micro Sol also works a treat. Allow drying time.
Then clear to seal it - again acrylic or Future. And I only tend to paint the sidewalls. If they are glossy, it's okay (esp 43rd... in 20th you may want to go to SG). I then leave that and touch the running surface with file to get rid of any potential gloss there.
Like I said, I don't claim this to be the ultimate solution to all tyre problems and YMMV, but it's worked well enough for me up till now.
And Jason - show us some WIP pics of that build!