I redesigned my large SIP model to be easier, faster and cheaper to build along with hold a larger water tank.
Step 1 - Take a 20 gallon plastic tub and drill a couple of drainage holes 1/2" at 6" from the bottom.
Step 2 - Take a 5 gallon plastic bucket (Home Depot etc.) and cut it just over 6 1/2" from the bottom and cut a 6" circle in the middle to be used as a support base.
Step 3 - Using a saw make 6 cuts at the lip about 1 - 2" wide each as shown for the water to irrigate through this support base.
Step 4 - Drill 1/2" holes through this structure to increase water flow.
Step 5 - This support base will be placed inside this first 20 plastic gallon tub bottom end up.
Step 6 - Take another 20 gallon plastic tub and turn it upside down. Drill 1/4" drain holes at the outer section, 6" hole in the center and 1 1/'8" hole for the 3/4" PVC pipe that will be your water tube.
Step 7 - Flip this container over and insert inside the first container on top of the support base. Cut a 2 ft piece of 3/4" PVC and cut off a piece at the bottom lip (taper it) so it does not sit flush restricting watering from flowing into the base.
Step 8 - Drill (2) 1/4" holes the side near the top.
Step 9 - Insert the PVC pipe (taper end down) into your hole your drilled in the support platform and secure the PVC pipe with a plastic zip tie.
Step 10 - Take a 1 gallon pot (Home Depot) and drill 3/8" holes in it to work as your wicker system. The picture here is smaller than use now. Make sure it is at least 7" in height.
Step 11 - Insert a piece of cheese cloth, shop rag or air conditioner filter inside the wicker basket to allow water to flow into but keep the dirt from entering your water tank.
Sept 12 - Insert the wicker basket and your filter material in the 6" diameter hole you cut going through the top tub, support platform and passing through the lower tub. Remove the rope handles from the top tub if you want to use a plastic tarp mulch to help retain moisture.
Step 13 - Wet your potting mix (not dirt!) and whatever nutrients (Lime, Mycorrhizal Fungi etc.) you want to add. Fill up the SIP and set your tree up centered inside it. I used 3 1/2 cu ft of potting mix to get it filled to the top. I could fit 4 cu ft if I made a dome letting the tree sit higher. I was able to fill my tank with 5 gallons of water.
Step 14 - Place your 4 mil thick plastic tarp over the top and secure it with either connected plastic zip ties. Tighten and trim the ends of the zip ties off and trim your plastic tarp.
Step 15 - Cut a full size 7ft x 7ft burlap sack half way down the middle to place over your SIP and secure it with a clamp and trim as needed. This protects your plastic whiskey barrel from degrading faster from the heat and protects the trees roots when reaching the outside of the SIP from being burned up in the extreme heat of places like zone 9 and 10.
(2) 20 gallon (22") plastic rope handle tubs ($8 - $9 each) $16
Support Stand (5 Gallon Bucket cut and drilled) $3
2 ft piece of 3/4" PVC Watering Pipe $1
1 Burlap Sack (7ft x 7ft) top cover protecting roots from burning in summer $6 (Home Depot)
Clamp for top cover $1 (Home Depot)
plastic Zip Ties $1 (guesstimate)
4 mm Thick Plastic Tarp Cover $1 (guesstimate) worth (but you have to buy a roll)
6" Plastic Container used a wicker $1 + (Home Depot)
Estimated Container Cost $30
Difficulty Rating - Moderate for some tools required