I have made flush hatches for my WR180. I didnt go the route of the straps as I felt my idea was more secure and didnt have the loose ends of straps dangling around. I have 4 bolts 1/4" thick protruding from the flush inset flange the cover sits on. These for bolts, facing upward go through the four matched holes in the hatch cover. I throw on 4 water tight washers and four acorn nuts and whamo - a very tight secure hatch.
It means I need to carry a tiny wrench with me, but its hardly obtrusive and goes in my gear bag with a little tether, along with binos, radio, gps - you get the picture.
The ultra clean-look deck fittings of it all make it appealing too.