Honda 1991 Prelude Owner's Manual page 116

Rust Prevention
Rusting is likely to occur in parts of the car where water is trapped
or where there is continual dampness.
Water will collect inside doors and body panels if drain holes
become clogged.
Water which seeps under or soaks floor mats will subject floor
sections to prolonged wetness or dampness.
Road dirt or sand, which collects and fills recesses on the
underside of the car, retains moisture long after the rest of the
car has dried.
The removal of paint and undercoating by stones, gravel, and minor
accidents immediately exposes metal to air and moisture.
Rusting is increased by high humidity and by the presence of
corrosive substances in the air or on the roads.
Salt used for road de-icing will coat the bottom of the car and
hasten rusting.
Localities with high humidity have greater potential for rust
problems, especially where salt is also present on the road or in
moist sea air.
Industrial pollution will accelerate the deterioration of paint
finishes and promote rusting.
Preventive Service
Check all drain holes in the doors and body panels for clogging and
clear if necessary. When washing your car, also clean the underside
of the car by using high pressure water;
inside front fender,
and under rear bumper.
After washing your car or after heavy rain, check for leaks. White
checking for leaks, lift the floor mats in the passenger, cargo and
spare tire areas, and check beneath them. Water can collect in
these areas and remain unseen for prolonged periods. Dry any wet
areas of your car's interior. Remove and dry wet floor mats. Have
leaks repaired as soon as possible.
After driving your car, wipe off any road dirt or salt on the radio
antenna, with it fully extended.
rear suspension,
above subframe,
inside rear wheel housing,
(cont'd)