When I relocated the flap on my KE70 ute to inside the tray, we cut the door/filler out of a Subaru Legacy wagon and welded that in. Obviously not what you want to do but the interesting bit is that a boot release solenoid from a Falcon (not sure what model, probably fairly generic though) hooked straight up to the Subaru flap. Would be worth checking how close a fit it is to whatever you adapt.
Callum
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