I recently was in the same situation, I noticed at the hobby shop they were selling 3M Brand Scotch MultiTask Tape as "hinge tape" It has a gloss finish, I used it to seal my hinge gaps on my Hangar 9 Extra 260 and it has been holding up very well.

To install it, I flexed the surface all the way one direction opening the gap up as wide as it would go. Then I took managable sized pieces of tape and a ruler to get the tape all the way into the gap. Then I used the ruler to squeegee (sp) the tape onto the sides of the surface and the wing. It worked out pretty well, a little time consuming but you can't even see the tape once it's on there. I've checked it several times and it has not cracked or pealed, and I'm using 3D throws on a gas plane.

I tried covering material but couldn't get it to look good and smooth.

The tape is about $2.50 at Wal-Mart.

I did not run the tape over the hinges themselves.

Don't use regular scotch tape because it will crack and fail. This stuff won't crease when you fold it over and seems to be very durable.