I purchased a relatively cheap glue applicator roller from Amazon (https://www.amazon.com/dp/B07T55Z18S?ref=ppx_yo2ov_dt_b_fed_asin_title), but it did not come with a cover. To prevent dust from entering and to slow down the glue in the hopper from drying out, I designed this cover which clips on the top. The included Fusion 360 file is parameterized for if you want to adjust it to other sizes. I printed in PETG as I mainly use that filament, but it should be fine in PLA and TPU as well.