I built a wood frame pond of similar size than yours. Too bad I had to take it down after a hurricane, but oh well, I learn a lot. Try to get a good quality pond liner, a 45 mil specs will do fine. When installing the pond liner, you will have to partially fill it with water, so it will adjust to the inside of the wood frame, then you can secure it. I wanted an overflow so the water would drain to the W/D. I was able to make a DIY bulkhead with modified PVC couplers 1.5" in diameter. Drilled a hole through the wood and through the liner. It was a gamble, but it paid off real sweet. Used plenty of silicone sealant before installing the couplers, even on the wood part. Installed the coupler. Let it cured, a second thick coat of silicone all around the outside base of the couplers on both ends. Water flowed flawlesly to the W/D without a drop leaking anywhere!
By the way, I'm also installing a fiberglass "pond" in my garage (see my avatar) of size 8'x4'x3' the advantage is that I don't have to do any work, other than drill bulkheads , plus it has a viewing window. Should get it delivered tomorrow....can hardly wait....I won't sleep tonight...
