Decal removal help please

[gofastsandman]

Taking off 20 yr old decals and replacing w/ new "old style" ones Bushwacker was kind enough to source. Thanks again Denny!
Sooo , I went to Harbor Freight and picked up a dual temp heat gun. 572/1076 degrees. I plan on starting on low to remove the decals.

Is there something I can spray on to loosen the glue as a helper? Will the heat damage the gelcote? Any and all help is ,as always, much appreciated.
Thx,
GFS