You should try to build your structure in such a way so you don’t have to use any sealants. If you do need to, there are only a few that are suitable (most will adversely affect the polycarbonate). Ensure it says that it’s suitable for polycarbonate on the back.
We can supply Laserlite sealants.
The following are also suitable:
HOLDFAST FixAll 220 MS
HOLDFAST FixAll MS Crystal