This is about as close as you'll get to an original:
The key to good adhesion is in the prep. Every last bit of the old decal must be removed, as well as all the old adhesive. I personally like 3M adhesive remover, it takes a little work to remove it with that, but it's gentle enough that it won't hurt the paint. Mineral spirits will also work. When all done, I like to prep the surface with rubbing alcohol before applying.
To apply the new decal, I recommend taping it to the trailer in the position you want it, with masking tape. It will be tough on the crimped aluminum, but line up the top or bottom to where you want it and then tape it down, making sure it's straight. Then, put a few bands of tape across the top edge to act as a hinge. Untape the other sides of the decal. Now do the final alcohol prep on the surface and dry it. Then remove the backing paper, making sure to hold the decal out away from the trailer. Using a plastic squeegee for applying decals, push down the decal onto the trailer, starting at that hinge tape. Work it in to any grooves in the aluminum as you go. When you've pushed it all down, carefully peel off the masking paper and tape, watching that the decal doesn't lift anywhere and go with the paper, which can cause a tear.
When you're all done, you can carefully work out any bubbles with the squeegee, just be careful not to wrinkle it. If you can't get an air bubble out, you can poke a small hole in it with a knife or pin and then flatten with the squeegee.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR