What mil gauge us the vinyl and is the adhesive made of silicone- butyl?

The tape is 6.5mil and the adhesive is actually a waterproof acrylic adhesive not silicone butyl. Hope that helps and thanks for your interest in Better Boat.

Could this be used to patch a hole in a trampoline?

Unfortunately a trampoline is a very difficult material to repair because it expands and contracts so much. We are not aware of a trampoline patch solution but don't recommend our repair tape in that use case. Sorry about that and thanks for your interest in our repair tape.

Will this work with sunsetter motorized retractable awnings? i have one with seams that are coming undone.

This will work. At the seams can be difficult but if you clear the area and lay it flat you should be good to go. Thanks for your interest.

Has anyone had any luck repairing a boat cover? Thank you

We think you will be happy with it but we completely stand behind our money back guarantee so if you are not fully satisfied just let us know and we can refund your order. Thanks for considering Better Boat.