I would be trying to determine just how bad the leak is. Many RV type windows are secured with a trim ring screwed from the inside. With the photo you shared I’d remove the interior trim ring while having someone on the outside keeping it from falling out. With a hard plastic putty knife then work it under the the outside rim to sever the butyl tape and remove the window. Once off clean the surface on the window and trailer where the tape was, apply new on the window surround and reinstall. Since it’s summer I would let the butyl tape rest for a few days and see if any more oozes out, then seal with Proflex sealant. Don’t use silicon sealants.