I've had good luck using DupliColor Automotive clear - but I ussually use DupliColor base...
But here is an example of a how the decals looked after applying the clear on the last one I did:
http://homeracingworld.us/viewtopic.php ... al+lee%27s
(shots of the completed job with two coats of clear are at the bottom of page one)
I haven't had any issues with "wrinkling" or "lift" - but I typically put one light coat on, then after letting that set-up, go over it with a heavy coat, using a can heated in hot water and it comes out glaaaaass smooth! :D
Good luck!