Choosing a Roof Box Storage Cover: Size, Protection and Conditions

Start with the cover’s job

A storage cover can protect a compatible clean lid from dust and incidental surface contact indoors. It does not support the box, secure it to a wall mount or turn a garage hoist into a complete installation. Decide how the box will be supported before choosing the fabric that goes over it.

The named Thule covers in this guide are indoor lid covers. They are not full outdoor weather enclosures or travelling accessories. A photograph of a covered shell cannot establish that rain, sunlight, damp or the underlying storage position is suitable for the actual box.

Our off-car storage guide covers support and handling. Use the cover as a separate finishing choice once the shell’s orientation, condition and storage environment have been settled.

Identify the exact shell and generation

Record the box model and size code, then check the current cover compatibility list and the box accessory instructions. Similar family names can refer to different shapes, while an older model may use a different cover from a newer box with comparable litres.

Do not choose solely by exterior length or a retailer’s small/large label. A cover’s elastic edge must suit the intended lid profile, and the complete instructions may identify specific models rather than a universal dimensional range. If the original cover has no readable label, do not assume a replacement of the same apparent colour is the same size.

For the examples used across this site, Motion 3 Sport, M and L are listed for size 1, while Motion 3 XL is listed for size 4. Those are model-specific examples, not a rule that every 300L box takes size 1 or every large shell takes size 4.

Resolve conflicting references before ordering

Force 3 L Sport illustrates why checking more than a broad size label matters. The current size 1 cover product page and Force 3 accessory instructions list 698100, while the current accessory matrix places Force 3 L Sport under size 2. The disagreement concerns that exact model rather than every box in the range.

Obtain confirmation from Thule for the actual box and cover reference before treating either size as a confirmed match. Keep the response with your parts record. Do not select the larger option merely to avoid asking; excess fabric can affect fit and access without resolving the intended compatibility.

If the maker updates a reference, use the clarified information for the supplied generation. A retailer review saying a cover stretched over another box is not equivalent to the manufacturer’s approval.

Compare size-specific indoor protection

The size 1/698100 and size 4/698400 examples are two versions of a soft indoor lid-cover approach, not different grades of weather protection. Their useful distinction is which exact lids they are listed to fit. Match the selected Amazon model number to that reference before ordering.

Soft fabric and an elastic edge can make fitting straightforward when the cover is correct and the lid is clean. Pull it into the position described by the instructions without forcing it across vulnerable hardware. Keep any storage pocket or loose fabric clear of mechanisms and the supporting system.

A compatible cover should not become an excuse to stop inspecting the shell, mounts or support arrangement. Remove or reposition it as required to see the relevant surfaces and check for damp or contact damage.

Assess the storage environment separately

A dry enclosed garage is different from a damp shed, open-sided carport or outdoor wall. Confirm the box maker’s permitted conditions and the support system’s intended location. An indoor cover does not expand those conditions.

Check for water entering at a door, condensation on cold surfaces and contact with damp floors or walls. Keep the shell away from heat sources or conditions prohibited by its instructions. Do not add a tightly wrapped plastic layer as an assumed improvement; it can hide moisture and may not be an approved arrangement.

Where conditions are uncertain, fix the storage environment or choose a different permitted location before buying fabric to hide the problem. A cover is usually a smaller decision than the suitability of the space beneath it.

Wash, inspect and dry before fitting

Clean the box using its manufacturer’s permitted method, then inspect the shell, lid edge and mechanisms. Loose grit under a soft cover can still abrade the finish during handling. Do not put the cover over salt residue or leave damp straps and bags inside the closed box.

Let all relevant surfaces and retained parts dry completely in a permitted position. Check the interior as well as the visible top. The cleaning guide explains why washing, damage inspection and drying should be separate steps.

Keep the cover compatible with the support system

On a wall mount or hoist, check that fabric cannot interfere with contact points, moving parts, retention or inspections. The shell must remain supported and retained exactly as its instructions require. Do not use the elastic edge as a lifting sling or pull on it to reposition a suspended box.

A cover adds no load capacity and does not make an unsuitable orientation acceptable. Where the storage-system instructions require particular surfaces to remain accessible or uncovered, follow that requirement rather than altering the support to accommodate the fabric.

Care for the cover and recheck before the next trip

Follow the cover’s own washing and drying instructions and store it clean between uses. Inspect its elastic and fabric for damage or contamination. Do not assume a washable cover can tolerate any temperature, solvent or cleaning treatment used elsewhere in the garage.

Remove it before fitting the box to the car, then complete the normal shell, mounting, lock and restraint checks. Keep its model reference with the box record so the next purchase starts with an exact identity. Reassess the cover fit if you replace the box rather than carrying a size choice forward automatically.

Sources checked October 2026: size 1/698100 product list, size 4 product information, current accessory matrix and Force 3 instructions. Confirm the Force 3 L Sport discrepancy before purchase.

Frequently asked questions