This was posted below,But I thought that I would post it again,I think that I entered the conversation a little late.
I spray future in the area where the decal will be applied,then I position the decal where needed,I then use decal solvent(solvaset)I wait an hour or two and the the decal set do it's job then I spray a thin coat of future over the decal let dry 5 or ten minutes and then repeat process. The next step is to airbrush a flat coat over the decal and let dry ,if needed you can shoot another layer of future over the top of the flat coat,only if decal edges can be seen then flat coat for the final time than weather the vehicle. This is the process that I use when using waterslide decals as you see in my images this process works quite well. Thanks
....Mrosko