does it make any difference ?

you build everything the way you do, & then you adjust the length
of the bungie cords.

another issue you should consider is the "dynamic range" of the bungies.

you should have enough flexibility left on the bungies to pull the covers
high enough to insert a hand & release them.

to achieve this I think you'll have to tie a bungie between 2 points
on the hull, like a string, & then pull it up & place it over the hooks
on the covers. so it will be 2 bungies.

the required pull down force you need also depends on the width
of the sealant (the area on which the pressure is spread).

look in my webpage, perhaps you'l find some more info:

http://homepages.go.com/~fl_pelican/home.htm

Erez