copy and paste this in the ext_config
[RAIN_FX]
PUDDLES_MATERIALS = roadnew?, road_patch?, new_tarmac, VIS_WAL?, ROAD, kerb, mosport_roadgreen, roadlines, pit_concrete, MOSPORT_DMG_GRASS, mosport_drain
PUDDLES_MESHES = rdedges, TRANSITION?, VIS_ALL_PATCH_BORDER, t1_waterchannel.002
LINES_MATERIALS = roadlines
SOAKING_MATERIALS = new_tarmac, ROAD, kerb, mosport_roadgreen, roadlines, pit_concrete, MOSPORT_DMG_GRASS
SOAKING_MESHES = rdedges, TRANSITION?, VIS_ALL_PATCH_BORDER, t1_waterchannel.002
SMOOTH_MATERIALS = guardrail, mosport_vehicles?, SEMI
ROUGH_MATERIALS = GRASS_CLOSE, Background, gravel_dirt
ROUGH_MESHES = grs_in_out_blend.001, SDTRAP_EDGE