Sealing one side of the gap works fine.

I have used hinge gap tape on a glow plane - really dumb idea. Adhesive not up to dealing with glow exhaust spooge.

I prefer using film - Ultracote 'cause that's all I use to cover my planes. If the fixed surface and the associated movable control surface are of the same color with no trim pieces crossing the hinge line then use the same colored film. If they are different colors or there's trim pieces crossing the hinge line use "clear" film. Ultracote has a light weight clear.

How? Cut a strip 1/2" wide just about as long as the hinge gap. Crease the strip in half and lay the "V" into the hinge gap. Seal one side or the other first - your choice. Then move the control surface to its extreme high-rate position. While holding it in the extreme position seal the other half of the strip. This will ensure that you have full control surface movement. If using Robart hinge points then it might work better to cut smaller pieces for the gaps between the hinges. Depends on how big the hinge bulge is. CA hinges - not necessary at all. Dubro nylon pinned hinges - maybe - depends on the build job.

If your exhaust is out the bottom then seal the bottom gaps. I'd seal the left side of the rudder.

If you're pretty anal about the look of the plane you can seal both sides as suggested earlier.