Assess the inside of the top, side by side and front to back. If the top has lip or an edge, assess the depth of that too. Cut two pieces of de-inch plywood in form and the size of the inside of the sides of your trunk. Add the upper part of the trunk’s depth to the pieces’ height, minus 3/4 inches from the top of plywood will add. Use a jigsaw to make cuts. Slide in to make sure they fit without forcing. Make the necessary adjustments.
Cut a piece of de-inch plywood for the dimensions of the upper trunk. Set this piece in the top. Make the 4-inch side of the slot parallel. This is used as a treat. Pilot holes of the top part with a 1/8 inch wood wick along both side edges. Frames 3/8 from the edge of an inch. Make at least four holes, spaced evenly along each edge.
Wicker storage bench tend to be brittle, and they will have to be made to prevent crushing your piece reinforcements. A few cuts to a couple of screws and a sheet of plywood are all still, and you will need to turn your trunk into a bank maintain storage. Your trunk will be tough enough at full maturity to sit. Get the measurement from side to side at the bottom if the sides are tilted in the direction of the bottom.