Using billy bucket, drag mud from lake and make sod walls, 200x200x200, like a sand castle effect, Stack the mud walls to 2m by 1.5 m wide, you need 150 of these, reinforce the wall with sticks pushed into wall, like a wattle and darb idea, the olden soddies did in Australia long ago. Make the fire place also of mud with dome, and chimney. The main pole is 4.5m long and the verndah bits 2m , no need to make whole thing warm just the sleeping part. Stack wood under the verandah bit. Only animal to contend with is the Tassy Devil, so do not cook fish on the fire, but elsewhere outside, 50mm away.