Definately tie down straps.
The cover gets difficult to stretch when it's cooler/cold making snaps a b#### to match. You won't have to drill holes into your hull. You can tighten the cover as much or as little as you want. If you change an accessory that sticks up, like a trolling motor, you'd have to reposition snaps. The list goes on and on.......
I would get the motor cover seperate from the rest - makes it easier to tighten the main cover securely for trailering.
Get the straps made a bit longer than you might expect - it makes it easier to grab hold of them when the cover isn't quite on straight.
Get a bicycle innertube and cut it into 2" lengths. Slide them over the main section of the straps when the straps are loose. Then, once you've got the cover on, slide the tag end of the strap into the innertube sections to keep them from flopping around.
me!