I've been building for quite sometime now and can tell you that plug will absorb water like a sponge , pretty much ruining it. No worries, you've made your first of many. Fish it and watch it swim Next time after drilling all the holes , you need to epoxy seal it. Epoxy not only seals it but helps to make it harder. 3 days later i prime it then paint then 2 coats of epoxy. I let it cure 2 days then rig it up. System 3 is my # 1 choice. Get pipe cleaners to hit that through hole and the weight holes. The idea is to stop water absorption because you can't stop intrusion.