I’d insert a sheepshank into the last run of twine across the frame, then loop the leading edge of the twine around the frame and back into the closest loop of the sheepshank, pull tight, then tie off with two half hitches.
Two Half Hitches
I prefer this combination over a truckers hitch because it is easier to dismantle and is less likely to deform your rope / twine.
A word of warning however... the sheepshank was developed for a time when ropes were made from natural material - the thicker and rougher the rope, the better a sheepshank will perform. The sheepshank knot does not work well with synthetic “smooth” rope, as it has a tendency to collapse. The truckers hitch is better for modern synthetic rope that is “slippery”.
The sheepshank is a little tricky to learn, but once you master this skill, it’s a versatile and robust knot that will become as valuable to you as a reef knot or clove hitch.