Roger, in the past, I have used a Pro Guard product similar to the Liquid Rubber you mention and it was indeed, satisfactory. Though a great product, I believe spot sealants and coatings are not truly comparable with a roofing "system" such as the RV Armor roof. It's apples to oranges. The only RV roof I recommend is RV Armor. You can’t beat the lifetime warranty and the cost-savings over time. If you factor in the typical and annual maintenance costs, let alone the hassle of having to take the RV to a service facility, it’s an easy decision for committed RV owners to make.
I would suggest you give RV Armor a call and allow them to provide you with an estimate to, once and forever, relieve you of all concerns regarding your roof. As they state in their video, you’ll never have to get up on that roof again.
After seeing RV Armor in person, and getting to know the company and the product, I consider all other RV roof maintenance products just about unnecessary, and simply not worth the time and expense it takes each and every season.