Ok, I decided to go with decals rather than using vinyl masks on the new classic plane. For a lot of reasons not the least of which is time. It takes the sign guy awhile to get them cut and I need to put them on soon. Question is coatings. I've used Krylon clearcoat, clear dope, catalyzed polyurethane and some sort of off brand clearcoat. All worked to one extent or another. Any thought on what the best to use is? I know the last time I had a lot of problems and ended up giving up on them and used vinyl masks. A lot of that had to do with the humidity level at the time. I also want to try shooting on a light coat or two then cutting them out of the sheet then shooting on another coat or two so that the cut edges are sealed. Any thoughts on that?

HUMIDITY is hitting the decal problem right on the noggin' and some folks use a hair dryer on low heat to help speed the drying process...however THAT just might lead to other  problems and that main problem is that the paint underneath the decal HAS TO CURE AND GAS OFF which might hinder more than help? 
With that in mind...I think it was either Mike Potter or Ben Madsen who always carefully pricked a variety of teenie-tiny pin holes on their decal sheets before slidddddddding them off onto the model. However, whether that helped or not...neither of those amazingly gifted scale model builders ever had a decal lifting problem that I know?

"I also want to try shooting on a light coat or two then cutting them out of the sheet then shooting on another coat or two so that the cut edges are sealed. Any thoughts on that?"

Yeah Randy, don't do it. I tried it on my first set of decals for the Tempest. The first two coats went on fine but after I cut them out & put on the third coat the clear went under the edge, between the decal & the backing paper & it ruined the decals. The second time I just put on two coats, trimmed & put 'em on there. The car clear sealed the edges just fine.

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Randy and all...

I find that giving the 'paint' on the model several days to gas out is a great help, of course. Don't get carried away overcoating the graphics with sealer, Krylon Crystal-Clear, or whatever you're using. Builds up thickness, and that means not only an edge to flat down, but more likely to crack or wrinkle over a curve...

Also, plastic display model builders use an inter-coat liquid - one I found is Micro Set, another may be named Solva-Set - lightly brushed over the area the decal will occupy, just before applying it. A kid's dimestore paintbrush is plenty adequate for that... Label instructions suggest that it softens the film substrate to help it lay down better.  When you're happy the decal is settled in as you want, dry the outer surface gently by wiping with a dry Kleenex, and let it sit, undisturbed, for a day or so to get the contact surfaces dry. Once it has done that (depending on the compatibility of the decal sealer with your final gloss top coat material) you should be able to shoot the last coat or so over the model, including decal area.

For larger decals, I squeegee out any air bubbles with a  damp Kleenex - working from center out of course - and gently! On severe 3D curves, it may be occasionally needed to punch pinpoint holes around the area.

I don't use decals anymore. However when I did I shot clear over them first and cut them out. So if I were you, I would shoot Urethane over them with dust coats and let cure. Cut them out and stick them down. Then shoot clear urethane over the top of them . Good luck.

I see that there is a lot of opinions here but this is what I use....maybe it will not work for you, but it has been fine for me. coat the decal with a couple of coats of clear enamel Rust-o-lem then after the application to the model, I am told, a couple coats of clear dope works great sprayed over the entire model.
Larry

I make my decals from Testors decal paper on an inkjet printer. After the ink is dry I brush on one light thinned coat of clear dope. Do not let dope get under the edge of the decal, or you will have trouble sliding it off of the backing paper. After the dope has dried for 6 to 8 hours, or over night, cut out the decals and apply them to the model. After they are applied they can still be removed by scraping a corner and pulling them off. After applying dope over the decals on the model they cannot be removed without sanding. This has worked well for me and the decals seem to stand up well.