This is mostly done from inside the RV looking up. You have to remove the vent cover of the AC and pull it down. Then look up in the hole at the edges and you can see the foam gasket. The gasket should be about 1/2 inch thick or more. If it's tightened down too tight it can cause a leak.
To tighten the gasket just tighten the 4 bolts you see when looking up. But again don't overtighten them, If they are already more than finger tight I would say no more than one half to one full turn of each bolt.
To replace the gasket you have to disconnect the electrical. Then remove the 4 bolts from the inside. Now go up on the roof and lift the AC up and out of the hole. Have a sheet of plywood or something to set the AC on so you don't tear the rubber roof. replace the gasket and put the AC back over the hole. Tighten the gasket down about half way.
As with most things these days there are a bunch of youtube videos on how to do the job.
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2001 Suburban 4x4. 6.0L, 4.10 3/4 ton **** 2005 Jayco Jay Flight 27BH **** 1986 Coleman Columbia Popup