Just an additional 2 cents to add to Mr Langs comments.
A butyl based sealer's ideal and certain types of urethane are OK too.
I use a primerless urethane system in my work and it does sticks like 'you know what' to a blanket,so clean up at a later date might be a problem.
Although you wouldn't have the same reaction problems as you would with silicone.

A urethane sealer that uses a primer base if used without the primer can usually be peeled off a gloss paint finish once it has dried fully.
The primer is intended for bonded glass applications where grip is as important as water tightness.
You would just need to make sure which one you used.

1950 Chevy Advance Design 3100 in Scotland
In the Stovebolt Gallery
More pix on Flickr.
I've definately got this truck thing in my blood ... my DNA sequence has torque settings
"Of all the small nations of this earth,perhaps only the ancient Greeks surpass the Scots in their contribution to mankind" Winston Churchill.