Spray foam insulation is a great product. Homes insulated with it can be some of the most efficient and comfortable homes built. I've been in plenty of these homes and can tell you that when spray foam is installed properly, they outperform 99% of fiberglass batt-insulated, stick-built homes. (I can also tell you that 73% of all statistics are made up on the spot, so please don't ask for documentation of that statistic.)
Liquid Rubber is generally fine when applied in one coat at a 20 mil film (42 sq ft per gallon) thickness and will still withstand extremes. That is the beauty of the EPDM polymer. A second coat would provide insurance where exposures are likely to be very extreme. Radical extremes in temperature where constant surface temperatures reach 250°F or above or -20°F or below. Warning, though, if the second coat is applied at the wrong time, it may create cracking, fissures or bubbling. The second coat should be applied either when the first coat is still tacky or when that first coat has had a chance to fully cure (up to 3 months.)
What more is that we also think it is one of the most durable among liquid roof coatings on the market. It can last for several years, working continuously in protecting your roof from outside elements, such as dust, leaves, twigs and debris that would otherwise damage your roof. When it happens, your roof might have leaks and cause discomfort inside your RV.