You might be able to get away with it Steve. I built a wood frame above ground tank for a customer last year. It is 5' x 9' x 4.5' deep. I shot 1/4" bolts through a pt 2 x 4, plus 1 1/2" into the concrete as the base along with stringers underneath. Then tied into them with 2 x 4 and 4 x 4 framing. 3/4" marine ply inside. All corners were 4 x 4 to 2 x 4, making them 4 x 6. Laid in the liner, tacked down the top, then fastened double cap rails all the way around. To make sure it wouldn't come apart at the center, I used 3/8" threaded steel and bolted it through the walls across the width of the tank above water level. I used pipe insulation to cover it so fish couldn't get hurt if they jumped and hit it. Bottom drain and skimmer are pump suction to an Ultima 6000. Unfortunately, that's all the room the customer had for filtration. But he also does about 50% water changes over the course of each week. He has a crazy fish load in there and his main pond (original reason for building this system)LOL!!!! Seems to be working just fine. He loves it!!
Good Luck with yours
Mike