Outer Armour is among the best - custom fit for your boat if they can still make one for the 2005 model year. It doesn't use straps and is suitable for trailering. Second would be the original Yamaha cover if you can locate one - but only suitable for covering/mooring not for trailering as it will rub on the gel coat. Third would probably be a custom cut cover from a local marine supply company that will measure and fit a cover to your boat, but again not suitable for trailering.
When you trailer the boat, remember the cushions inside the boat need to be held in place or you may loose one from the buffeting winds. Through town at 30 MPH is not an issue, but highway speeds may suck them out.
If you've never driven a jet boat, they're a blast to drive kinda like a big jetski, but much more comfortable. They handle differently but effectively once you learn how. Google is your friend for this info. Note they're reasonable for cruising and towing, but are not designed for maximum high speed performance as the jets tend to "plateau" at the upper revs as they struggle to suck in water fast enough to produce more thrust to overcome the hydrodynamic drag of the larger wetted boat surface. Jetskis can zip along because they have very little drag, but a 21' boat has a lot more surface drag. If top speed is your goal, a prop boat is your answer. But if tubing, skiing, wakeboarding, and cruising is what you want, a jetboat does it very well.
Lowering the tower is very easy with 2 people - just loosen the retention handles and the second person can easily hold and lower it, it's aluminum so it's not too heavy. Do not trailer with the tower lowered, as the support cables are not intended to handle the vibration and shock of movement during transport on a road/highway. Keep the tower raised unless storing it.
