I have seen posts that people are using 3M 99 Super adhevise to glue down tops. Will this hold? If so, do you spray onto the backing of vinyl or to the metal?

I plan to garage my Elky all the time so no moisture would get in except to wash it.

Use the glue on both surfaces. It kind of works like contact cement, but with a longer 'working time'. Let it set up and dry before mating the surfaces together. Read the other post on vinyl top installation.