Jay,
I flew my initial test sorties on my IV-P with electrical tape but it didn’t stay in place. I did this because I didn’t want to make a permanent installation until I was sure I didn’t need to adjust the wing angle of attack on one side or the other… (fortunately did not)
For my permanent installation, I filled the gap with clear silicone and have been very pleased with the results after 3 years of more than average flying. A couple of tricks: Prepare a consistent gap..mine was 3/16” before painting, and worked well. Apply the sealant after painting. Use masking tape or electrical tape on both sides of the joint, about 1/32” or closer to the edge, to make a clean line. Use plenty of sealant, but try to keep it from dripping down between the wing and fuselage on the top side. I use a piece of wire inserted in the gap and extended under where the sealant was being applied to force it to the edges on each side. (2 people make this easier). ASAP after applying the sealant, use a plastic spreader to make a smooth and consistent surface. Let the sealant “skim over”—a few minutes—and carefully remove the tape before the sealant is fully cured. DON’T try to improve your initial application with your finger or tools…it only gets worse…
Good Luck.
Bob