King canvas can be hit or miss. I ordered King canvas for my 25, because my canvas guy was too busy to get the job done in time. What I got was inferior. The seams were not all not knifed and none were bound. There were some other issues.
The King Canvas I have on the current 22 is decent--not perfect fit--but adequate.
If you want really good canvas, then find a good canvas worker, and have them do it. If you want some education see
http://www.sailrite.com Also see
http://www.glenraven.com/en_us/solutions/marine Probably more than you want to know--but it will help in the decision process.
Also consider what material. Sunbrella is the most common. Be cautions some folks use Chinese material. Sunbrella folks tell me it is not made in China, but it is possible that Glen Raven Mills (maker of Sunbrella) has some similar material which is inferior…There are combinations of acrylic fiver with a backing which are more waterproof.
Also consider the thread. Most are sewn with Dacron--good for several years full time up. If you want a thread which will last the length of the cover (10 to 11 years full time exposure), consider Tenara. It is more expensive (much) and harder to work with, but good for 10 years! It is made of a Goretex material.
Things I would look for in your boat: Free standing top, with at least a narrow panel zipped out in the front. You can be in some very hot muggy weather on the gulf coast, and you want the air flow under the canvas, so it is not an oven. For entrance, it is better to have two parallel zippers on both the side and the top. Start the zipper in the center for both sides. Same of sides, so you can roll up the side. I also like having awning rail on the forward edge of the side, so water does not get in. Have SS tubing, not Aluminum. Use SS hardware. You may have a choice of 3/4", 7/8" or 1" tubing. I would avoid 1/2 tubing. If you have adequate braces, you don't need forward bracing--one up and down right behind the entrance will be fine for both the front and back (gets away from the straps). See the my album on the Tom Cat 255. This was a very well made camper canvas. The worker spent several hours on the boat doing custom fitting, and getting it "right". I intentionally had small windows on the side--there are pluses to larger windows--and that is more light, and when you have insect screens ("No See em screen is better, especially for the Texas and Gulf Coast), as well as the clear vinyl. There are also different qualities of clear vinyl, They range from 10 mill (or gauge) (don't consider this) to 40 Mill in rolled vinyl. Then there are sheet vinyls which are Pressed and polished--these are optically clear. on up to "Strataglass". I have a friend who is a sailmaker who has used Lexan (not easy to sew), but if you are going around the world--worth it.
So lots to think about.