I'd remove the battery, let it sit for an hour or so, mix bleach and water about 50/50 and put in a trigger spray bottle. Put on nitrile gloves and spray down the relay box. Remove the relays and spray it down again. Wait 15 minutes and rinse with clean water. Dry out with a hair dryer and put it back together. Make sure you dry it well and you won't have any corrosion problems.
This way nothing will be airborne.