On several aircraft at Reno and elsewhere, sailplane gap seal material is
used.  Trip tape also.  Any sailplane supplier will have it.

A few things should be considered before using it though.  First, if the
aircraft requires the aerodynamic balance of the exposed portion of the
control surface that the gap seal will cover, it's not a good idea to use the
seals.  At least one aircraft I know of experienced severe handling problems
when the aerodynamic balance was sealed.

Next, we have to worry about the things coming off.  They are quite strong,
so if an end peels it will create a streamer that will bet the heck out of
the aircraft until the whole thing departs.  Ask Dave Morss about this on the
winning L-IV from 2000.  Put it on in small pieces, only a couple feet long
each.  If a piece lets go, it will tend to depart easier instead of trailing
and thrashing.  Pilots who have experienced this report it to be a religious
experience.

Last, there is significant evidence that they really don't do that much.  On
the drag reduction program for a major airliner, the addition of gap seals
was quantified at 0.2% of total aircraft drag.  Not much for all that hassle.
 Trip tape properly placed can make a lot more difference.  Wing fairings
make far more difference.  I sell both, but I prefer to give people more for
their dollar.

Eric Ahlstrom