Remember, it’s single copy so the expression level will be markedly lower (10-100x). Are you sure you could detect that amount? You could also try making a GFP fusion and see if you can detect fluorescence. In my experience, soluble mCherry expressed from a MosSCI insertions, even from a promoter that is fairly strong by high-copy transgene (<5ng/ul injected, easily seen by a dissection scope), is barely detectable at single copy even under a compound epifluorescence microscope at 100x.
I would recommend trying a 3xFLAG IP against your strain vs. a control to see whether you can enrich your protein to levels that are detectable by WB. You could even try this as a denaturing IP (solubilizing in 1% SDS and then dilute up in RIPA buffer minus SDS). Do it in parallel to your over-expressing strain.