I have a 2007 Denali fiver that may need the roof re-coated. I did my spring maintenance re-calked some cracks in the rood sealant and did a good inspection.There were no leaks. The roof is still white but getting a ruff texture. I have been reading about people that used Henry 887 to re-coat the roof. Has anyone used this and how has it worked? How hard is it to apply. The RV is 32 feet will one gallon do the job? Thanks in advance for your input.