My go-to roof type sealant is Eternabond tape. I prefer it to Dicor, because if you apply it correctly it will last a LONG time and will not leak. Dicor will eventually start cracking and will need to be reapplied. My sister's 2015 Lance trailer had cracked Dicor all around the vents, and was leaking every time it rained. We stripped all of that off a couple of years ago and replaced it with Eternabond. Hasn't leaked since.
I applied Eternabond tape to my truck camper roof over 15 years ago because its two lateral metal roof seams were leaking. It hasn't leaked a drop since. And that part of the roof is depressed, so every time it rains there is a pool of water up there right over that Eternabond Tape. I also have a 29-foot 5th wheel that I applied it to, and it hasn't leaked since then either. That was probably 12 or 13 years ago.
Having said that, I would not apply it in 40-degree weather. It works best when applied during warm days - at least 70 degrees, I would say. They say in colder weather it can still be applied with their primer, but honestly I would just wait until it gets warm. It is bulletproof when applied to a thoroughly-cleaned surface while it's warm out. Sticks like nothing you've ever seen before (so don't get it on anything you don't want it on). It's bonding strength is activated by pressure - so get a small roller to press it all down after applying. You can do this with your fingers too, but it's quicker and easier with a roller.
Cover your roof with a tarp if you can, and wait for warmer weather to apply the Eternabond. If you do it right, you probably won't ever have another leak.
