I tried to research the "wet method" but could only find info for installing decals on the side of cabinets - nothing about Mylar. I didn't use Rapid Tac either. It sounds like you are as concerned as I was about getting the Mylar down properly without having it stick prematurely where I didn't want it. I Mylared the entire playfield after applying a good coat of wax. First I cut the Mylar to size leaving the backing on of course. Then I taped the Mylar down to the edges of the playfield, enough to keep it in place and from moving. I made sure to get as much slack out as possible. I got the alignment as perfect as I could then I then began peeling the backing off 1"-2" at a time, just enough to be able to get it to stick to the playfield. I worked from the middle out to minimize any air bubbles. I then repeated with the next 1" -2" section after the first section was applied.
There are tools to "roll" the Mylar onto the playfield - don't know how well they work. I tried using a putty knife but thought it was scratching the Mylar so stuck to fingers and fingernails, primarily my thumb. I pressed hard and ended up with sore thumbs but no big bubbles. Several times I found bubbles in the section I had just put down but the Mylar was removed easily enough and then set back in place. It turned out to be easier than I thought but you do have to be careful. Get it wrong at the start and your Mylar will be crooked when you get to the end. I started at the top of the playfield. That way I could have more practice before getting to the more noticeable area in front of the flippers.
Getting the playfield cleaned and waxed is important - you don't want to Mylarize any mosquitoes for posterity!
There are lots of people who don't like full Mylar on their playfield. My priorities lie in preventing ball swirlies and protecting the art work for years to come. I like mine - even on a 1969 Williams EM Expo.
This is a pretty good "how to:"