I have a kt 30 cannot tighten brackets no more engine slides around any ideas ?

Use a little aluminum foil in between

Doble side foam tape.

Won't it melt or be ruined due to heat?

First I would ask My dealer....your strap shouldn’t be loose when tightened...while I don’t own a K30 none of my KingTech are loose in the strap...unless I crash the plane, then I get a new strap at the same time that they check or repair the motor for me....