Try looking up JCWhitney.com that is where I bought mine. Yet if the manufacture stopped making it, you are out of luck. You have to call JcWhitney, or use their online helper to look up the part number. Who knows the manufacture might still have a couple of gallons on hand? Worth asking for it. I used about 4 gallons on my 30' long RV.
As for the patch, I would not recommend coating the fresh sealant with Herculiner or anything else. If it comes off easy, take all you can get off now, and then coat the bare roof with Herculiner. If it is stuck there, don't try to remove it, just coat with Herculiner or another product.
I did find a couple of places where the Herculiner has leaked, mostly because I applied it thin in that location. Also beware the inside the RV will smell really badly once it is applied for about a week. I lived in mine, and had to run all 3 fantastic fans all night long, impossible in this 46F weather now, but worked great in So. California in May, with overnight temps hovering around 65.
My suggestion is if the Herculiner is not available in white, look at the video of the RV roof sealant at this site, and then apply that. One guy with a 38' Bounder mixed up 1 gallon for his roof, went around all the patches and sidewall seams, around the A/C. Then next morning mixed up a 5 gallon pail, then finished the roof, had some left over to re-seal the seams and sidewall joints, and seems to be holding up pretty good. This particular 2 part sealant has a "Pot" life of more than 4 hours, and can be extended by placing the container in a refrigerator. However it must be over 55F to cure, if it drops below that temperature, it will stop curing until it is warmer outside.
http://www.epdmcoatings.com/rv_roof_repair.htmlFred.
