RE: Boomerang Sprint Build Thread!
I guess I have to chip in here.
I use only thick CA glue (Zap A Gap or similar) and we have NEVER had one of the intakes come loose. The airflow is so easy through the fuselage that the side pulling forces are minimal on the intakes, certainly not enough to pull them off at any speed.
When I and later another builder filled the bottom gap with some kind of filler, it was so much less neat and tidy than leaving them as they were that I never used it again.
Strip the cut away covering about 1/16" (1.5mm) inside the line of the intake before fitting it, including the top line across the cutouts. Using CA means you can hold the top line tight against the fuselage side as it hardens and make a tidy job of it. It takes me one hour or so, start to finish, to fit the intakes, including stripping the required covering off. If you fuss over it you will not improve the simplicity and the tidy result.
A touch of white or silver added inside the front inch or two of the intake mouth before fitting it is a good idea. This will be factory added in future kits.