A good and very solid, secure option is made by DiamondBack Covers. I actually bought one to load my ATV on and tow my TT. The DiamondBack ATV cover I have can support 1600 lbs of weight on the cover and it is locking. DiamondBack also makes HD covers if you don't want to load ATVs on them. But importantly, the have risers that can attach for cross members which would be perfect for long kayaks, canoe or anything else. Downside is they are not the cheapest thing out there but for me it was worth the money.
DiamondBack Covers
I love me some land yachting