I have numerous planes with cowls, that eventually wind up with holes in the cowl oblonging and with screws that won't hold. I have tried putting CA hinge material under the cowl and the rubber backed washers. Velcro works in some situations, but distorts the cowl some. All hold for a little while but they also loosen up and either fall out or strip out. If some of you have ideas on the a better way please chime in and maybe some with pictures on what works for you. The best way so far for me has been with cowl rings attached to engine bulkhead, can't do that with all planes though.