thats the reason i used the abs pipe, silicone doesn't mix with plastics too good. i have some ideas for bigger ones, so if you need any ideas let me know.
Your idea of making it into tree stumps are great cause that would make it aesthetically appealing and also give it some weight so it doesn't float. How would you hide the powerhead though? Very nice idea man!
just build a fake rock or small stump with a hole for the output on the powerhead. i'll probably do one later, going one day next week to look at a couple 120gal tanks, if i get one i'll build the filtration like this.