Spray the TT surface with a fine water mist. Apply the decal over the mist. Slide it to EXACTLY where you want it. Then, using a plastic straight edge, a medium size pan-scraper will work, start in the middle, and squeegee the water out from under the decal, being careful not to leave an air or water bubbles behind.
If you leave a small air or water bubble, and you can't work it out to an edge, try a small pin to let the air or water out, then squeegee it flat.
This is how the striping and lettering on fire apparatus is done.
2014 RAM 2500 Laramie 4x4 Quad Cab w/Cummins Turbo Diesel, 2009 Rockwood 2607, and 3 'yaks!
300W of Suntech Solar, a Rogue MPT-3024 Controller, and a Xantrex PW2000 Inverter