Be aware that different brands of sewer hoses have different diameters of fittings. I bought a pair of Camco sewer hose wrenches only to find they didn't fit our hose. I need to get some that will fit because with every passing season I'm finding it harder to separate the hoses & fittings.
The ones I bought were these orange Camco ones. Are the strap wrenches being referred to these yellow JR Products ones? If so, they are supposedly flimsy and break easily. I haven't found other ones that are available. An oil filter strap wrench would work well but too heavy and cumbersome to me but an oil filter wrench *might* be okay. May try some silicone spray. Someone out there made a wrench out of alumium flat bar as below.