I built this tank out of 1/2" all the way around and had a floating plane in the bottom for strength. You might be able to get away with 3/8" but I like rimless and went 1/2" for peace of mind(it's so strong that it's going to last 10 years or more).I also used RTV103(black) and its thick-it's not a true silicone as it's a paste. VERY VERY strong. All I use is tape and alittle elbow grease. Tank is 25"x21"x16" running 2 month no leaks
This is tank is planted but I just don't have any recent photos