I set up my new diy cat tarp in the yard today. I used the Permatex flowable seam sealer that was recommended in another thread. I only sealed the outside, though. After about six hous of drying, we had a rain storm come through. I went out and got under the tarp. I noticed at one end, it was seeping inside. So, after the storm passed and the tarp dried, I seam sealed the underside of the seam. Is this ok? Are both sides normally supposed to be sealed or just one?