After 19 years of my 5th wheel sitting in the sun it's time to look into coating the roof. Like you I have found the most expensive products are the ones recommended by everyone. These products are sold as solutions for RVs.
I started looking for products for recoating EPDM membranes and discovered Henrys Roofing products has a Cool White Coating (Henrys 280DC) for use on EPDM roofs. When you read the specs it sounds just like the Dicor, Eternabond and other "RV" coatings
Henrys also has a tape for repairs Henrys 297 as well as a sealant Henrys 288
It's a lot less expensive than the "RV" coatings. I plan to give it a try in a few months.