Use of Weather-Strip Material to Prevent Water Entering Thule Rooftop Cargo Box

Updated 03/05/2018 | Published 03/03/2018

Question:

i was told that you could weather strip the boxes interior so that driving rain doesnt get into the box. i just drove through such conditions and some water did get in. not a ton, but enough to cause mildew if left unattended. if i can weather strip the inside without causing issues with opening and closing, please detail how its done. thanks

asked by: Fawn

Expert Reply:

Virtually no manufacturer actually wants/encourages owners to modify their products; this is certainly true for Thule and their various cargo boxes. My contact there advised that Thule cannot recommend making such a change although I do understand your interest in making your rooftop cargo box as water-tight as possible. It is all but impossible to make a rooftop cargo box totally waterproof.

My Thule contact did say that on older cargo boxes that have seen a lot of use sometimes the front hinge/lid support can develop a bit of play. This little bit of wear can sometimes allow the front edge of the box to "fish mouth", as they call it, meaning that high wind causes the top and bottom portions of the box to separate. In certain conditions that could allow water to enter the box.

If you want to remedy this issue you might first consider replacing the hinge/lid support with a new one that might provide a tighter fit of the top and bottom parts of the box. All hinges for Thule cargo boxes are shown on the linked page.

While I cannot officially recommend modifying the box # TH6356B, if you are going to do this you might focus on the front edge of the box for your application of weather-strip material. Most hardware stores offer several widths and thicknesses of weather-strip with a pressure-sensitive adhesive on one side. Be sure to clean the box surface with an alcohol wipe to remove any oil or other contaminants before you apply the strip material.

I suggest you apply this to the front of the bottom part of the box, on the inside of the box, so that the edge of the weather-strip is slightly higher than the edge of the box. Please refer to the linked photo.

expert reply by: Adam R