Dense clouds and TAT between -4 and +3 are almost a guarantee for wing icing, on all types.
Be VERY careful regarding the wiper bolt " trick". Wing icing will occur while the bolt is clean. it is NOT a good indicator. if there is ice crystal accumulation on the lower part of the central windscreen, there is indeed icing on the leading edge, but again, be careful. When in clouds and in temperatures around Freezing TAT, Wing icing is possible and wing lights should be ON and leading edge checked visually every minute.
All too often do I see too much trust in this "wiper nut" method which is absolute tosh.