Storing Your Classic Car

Why storage matters — the humidity principle

The single greatest threat to a stored classic is corrosion, and corrosion is driven by relative humidity and the dew point. Whenever the car's metal is colder than the surrounding air's dew point, moisture condenses on and inside it — into seams, box sections, under carpets and inside the exhaust — where it drives rust from the inside out. The aim of good storage is therefore a stable, dry environment (RH ideally below about 55%), not simply a warm one. Warmth on its own can actually make things worse if it creates temperature swings that push cool metal below the dew point.

Secondary risks compound the moisture problem. Tyres develop flat spots when the car sits for months on one contact patch. Brakes seize on if the handbrake is left applied. Fuel goes stale and, in modern E10, absorbs moisture that can harm classic fuel systems. The battery flattens and sulphates. Rubber seals, hoses and tyres perish with age. Rodents nest in exhausts, air boxes and carpets. And any damp, still corner of a garage will grow mould on leather and carpet. A good storage setup answers all of these together, not just the temperature.

Winter storage — the main UK season

Most UK classics are laid up from roughly November to March. The checklist below is what a careful owner does before shutting the garage door. Treat it as a routine, not a one-off — the same preparation done every year is what preserves the car.

Summer storage

Summer looks kinder to a stored classic than it really is. The threats are different, not smaller. Direct sunlight fades paint, cracks dashboards and hardens rubber and tyres, so keep the car out of direct sun. Warm days and cool nights swing the temperature through the dew point, so condensation is still very much a summer problem. A cover trapping heat and moisture over a still car will grow mould on leather and carpet, so ventilation matters as much in July as in January. Pests are more active in summer; fuel evaporates and stales faster in the heat. And portable/temporary garages can overheat spectacularly in summer, making venting the ends and using a breathable inner cover essential.

Heating in winter

The goal of any heating in a classic-car garage is not warmth for its own sake. It is to keep the car's metal reliably above the dew point of the air in the garage, and to avoid the large temperature swings that themselves cause condensation. A garage that is heated in the evenings and cold overnight is often worse than one that is simply cold all winter.

If you do heat, choose gentle, consistent background heat — tubular greenhouse heaters, a frost-thermostat oil-filled radiator, or dedicated frost heaters — and pair it with sealing gaps and insulating the space. Heating a leaky, uninsulated garage is expensive and largely ineffective.

The honest trade-off is this: a sealed, insulated garage held at a steady temperature 24/7 works well; but many experienced owners prefer to keep the space cold but stable and dry, because cold air holds less moisture, and to control humidity with a dehumidifier instead. Both approaches can produce a corrosion-free car — what fails is the middle ground of intermittent heat in a draughty space.

Dehumidifying

In most garages, a dehumidifier is the single most effective piece of storage equipment you can buy. It attacks the actual cause of corrosion — moisture — rather than the symptom.

Two types of dehumidifier are common, and the choice matters for a classic garage. Refrigerant / compressor dehumidifiers work well in warmer conditions but lose effectiveness sharply as the temperature falls, because their cold coil ices up. Desiccant dehumidifiers use a moisture-absorbing wheel and work well down to near freezing, which is why many classic owners in unheated UK garages prefer them for winter use.

Set the target humidity at or below about 55%, run a continuous drain to the outside where possible so the unit does not switch off with a full tank, and seal gaps and insulate the door so the unit is not fighting the whole street. Add moisture-absorbing crystals inside the cabin and boot to prevent interior mould. Always use a breathable cover on the car itself — never a non-breathable plastic sheet, which will trap condensation against the paint and rot the panels underneath.

Portable / temporary garages (e.g. Clarke's)

Portable garages — typically a steel tubular frame with a heavy-duty PE or PVC cover — are affordable, quick to erect, and a legitimate option where there is no permanent garage. Brands such as Clarke's are widely used by classic owners. Used correctly they can keep a car dry for years; used carelessly they can rust a car quickly. Three things decide which happens.

Airflow bubble systems (Carcoon and similar)

An airflow bubble — the best-known being the Carcoon — is an inflatable enclosure that isolates the car in a clean, stable, ventilated micro-environment. A base mat and a clear cover zip together around the car; low-wattage fans continuously push filtered air through the enclosure. The airflow keeps the atmosphere around the car moving and dry, which resists condensation, and because the bubble surrounds the underside as well as the paint it protects the chassis and floor as much as the bodywork. Most units run a short "drying" phase first — air passing over a warm car strips off residual moisture — then settle into a steady storage mode.

There are several variants. Traditional Carcoon bubbles have no internal frame and simply inflate around the car. Framed drive-in versions hold the cover clear of the car, which some owners prefer for regular access. Comparable products from other makers, such as the Airflow Airchamber, work on the same principle.

Product references

The items below are the products naturally referenced above. They are listed factually and neutrally so a reader can recognise the category — specific recommendations and links will be added here later.

Storing a classic car FAQ