NotMyName,
if the ecu's been waterlogged it'll have caused all sorts of shorting problems.
The best thing you can do is, using something like Loctites electrical contact cleaner, clean all plugs and connectors that are likely to have been drenched to ensure there is no water in anything. The slightest bit of water will play havoc causing shorts across system plugs.
Like AntGTD says, the soundproofing will hold twice its weight in water and a dehumidifier just wont manage.
Strip the interior if you can, remove as much excess water as you can and then shut it in a garage or somewhere similar with the dehumidifier and empty it often.
Check your intake system to make sure there's no water in it.