if you seal the holes on the rear of the td5 ecu that is a step in the right direction for waterprrofing it, also if you give the throttle pedal a spray of wd40 etc & same with the relays, it all helps,
i have the ecu in the roof of my challenge truck & the throttle pedal is on top of the dash being driven by a cable from the pedal box, the only thing thats lower than chest height is the standard relays & fuse box which can be reasonably waterproofed in standard form, or swap out the relays to waterproof ones & pack the fuses with silicone grease