Anything is hard to pound in out of a jon boat. Thought you said it was in only 2-4 foot of water? In that case, do what I do, which is carry a 10 foot aluminum step ladder with you, place it on the bottom and climb on and pound. Works quite well. Another thing I do, prior, that helps to make sure the blind is "square" is to cut out the bottom out of 1/2 or 3/4 inch treated plywood (most of the time I make a 4' x 8' whole piece as the bottom), notch the corners, plus one 2 feet over at the back for the entrance ladder for the 4x4's (cut the notches 6 X 6..important), float the plywood on the water and drive in the posts. It's a two person job, one to hold the post vertical and plumb and to keep the post in the notch, the other to pound. After that, remove the plywood( you'll have to lift up on one side to get it out), mark the amount of 'freeboard' you want on the posts where the sills will go (according to whether you have any fluctuation in water level) and nail or screw your treated 2x6's to the outside of the posts. (Use of a pneumatic nail gun makes it a lot more easy) Your plywood bottom will now be able to rest on the sills since you notched them 6 inches. Then place your floor joists across the short width (4'). I generally cut them on site as they may vary. Then drop on the bottom and nail the bottom to the joists. I usually make my ladder out of treated 2x4's and nail it to the 4x4 at the corner and the one 2 feet over for the opening. Top rails, seat and shelf along with wire fencing to attach camo is the last to be added.
Too much info?
Here's the last post blind I put in the swamp. I used round 4" posts so you don't have to keep them so square when you pound and makes it a little easier. The ladder post (on side) was a 2x6 which was pounded it and the ladder nailed to it after the other posts were set. Just as easy. Most of this stuff was used, treated, hog pen lumber (2x6's). Blind still stinks!
Click to enlarge