I recommend at least 3/4" plywood for the templates, 1/2" is too flexible for big j-bolts. Here goes, I'll try explaining it without a pic, so bear with me. This is how we do it, maybe others have a better way. You'll need some drywall screws and a short chunk of 2x2, maybe 6-8' long or so to cut into pieces.
1. Cut two pieces of 2x2 roughly a foot long. Put each piece flush with the top of the sono tube laying horizantally 180 degrees from each other, on opposite sides of the tube. This is on the outside. Run drywall screws in flush from the inside of the tube out into those pieces. Don't overdrive the screws or it'll distort the tube.
2. Now lay two 2x2's across the top of the sono tube long enough that you'll be able to screw into the top of both 2x2's you just installed in step 1. You'll lay your template on top of these boards. You want the template just wide enough to straddle the 2x2's and still be able to clear the nuts/washers on the j-bolts. Put your j-bolts through the plywood template, nuts/washers top and bottom to secure the j-bolts. Drop the template on top of the 2x2's, screw it down, then screw those 2x2's to the ones on the outside of the tube.
3. Pour your concrete. Rough finish it as best you can up against the 2x2's that are laying across the top. Let it set up for a bit. Maybe 30 mins or so. Come back with a sawzall and cut the 2x2's off flush with the edge of the template and get rid of them(you may be able to unscrew these 2x2's from the template and slide them out, but we always cut them. Just be sure your j-bolts don't sink if you decide to completely remove them). Now you should be able to put the final finish on the top of the pole base with only the square template left in the middle. Use a little water sprinkled on the concrete to bring the cream out and let you finish the top a little easier.
4. Don't forgot to pick up an edger the same diameter as the sono tube you're using. Vibrate the crap out of it if you can, wet the mud up a little, and rubber mallet it good to keep the air pockets away. A lot of times I don't have a vibrator, so I'll just rubber mallet it good.
