Taping/sealing hinge gaps
I guess you could use tape or covering. Covering would be my choice as it is lighter, could be matched to the color of the plane and is ready for immediate use. If you used any self-stick material/tape simply spray the area down with water or a mild solution of cleaner and get the tape in place. Then wipe it down with a soft cloth or facial tissue to weep up the moisture and then let it set for a day or two
Sealing the hinge gap doesn't necessarily make things stronger, but I guess it could help a little. The main advantage is the control surface does more of what it is supposed to do...control. To put it simple, when there is a hinge gap turbulence is created and some of the air goes through the gap instead of staying on the side you want it to...the larger the gap the worse the problem can be.