baby powder can be sprinkled around to help find water leaks. the water will make tracks through it, leading back towards the direction of the source. you don't need much. just a bit around the edges of the floors and then use the hose to try and make something leak. any and all gaps in the sheetmetal are suspect! I've had everything from a bad firewall plug, to the windshield, to the very top of the door allowing rain in if it came from juuuust the right angle.