For a sump you will be fine making it yourself. Notice Ive made a few sumps but i paid James at envision acrylics to make my custom tank. There is reason for this. From ten feet away you cnat tell james didnt make my sump. From two feet away James would be insulted(or just outright laugh) at any comparison. ; )
AS far as the 3/8" for a sump that size it will be fine. I recommend eurobracing it or simply bracing it like i do mine which is less obtrusive than a lip all the way around. i simply bond both sides and the center baffle with a 2" strip of acrylci and then a 3" triangle on each corner.
Works great and you dont have the lip all the way around to deal with.
As far as using 3/8" scrap for my rock lifts.........not really. The 1/2" is kinda mandatory to really hold the rods well and still have it interchangeable and not have to glue the rods in place. Im not sure i would want to go with 3/8 even if you did glue them to be honest. You COUOLD use 3/8 for the cross braces and the 1 1/2" pieces that go under the rods, but the 1 1/8" strips that hold the rods needs to be 1/2". Call James at Envision......hes local to you and he will either be able to sell you some scrap 1/2" or you can just call some local supply place for their scrap. If you have no luck PM me and i can give you some for my cost + shipping. You shouldnt have a hard time locating it in your area though.
3/4" rods
Here is a bunch of info on how to do it.
http://www.melevsreef.com/allmysumps.html
personally i dont like any of his sump designs becasue i hate refugiums and dont use them. But he has a ton of great info there regardless of how exactly you configure whats inside the box.
It looks like I may need some sump modifications but we'll see. I still wouldn't mind trying to build a sump if acrylic wasn't so expensive. I think that was the real deal breaker. I didn't want to spend a ton on acrylic only to botch the job up. I'll start with little sump modifications.
