Ahh nice, yea I'd go according to the BH's you decide to use, they take up lots of room, so let that help as a guide as to how big it will be. Two 1" BH's will require 1 7/8" hole plus you need room to tighten the big nut, I'd say go at least 4" deep & 10" wide at least. If you drill glass, I just had my 58G sump drilled for a 1" BH, he used a 2" bit I use the heavy duty BH so if your using the regular BH then I think it is 1 5/8" hole minimal. I took it to a glass shop & it cost me $10 for one hole & they polished it also, way cheaper than buying a bit, he had a special drill press with suction cups for glass to do it, way better than me trying to do the same. I also had them cut some plexi glass for the baffles I made, they were around $9 each for 12" x 17" x 1/4", which was reasonable. Oh yea as Krish said if the bottom is tempered then you need other ideas!
My tank is getting there...I have another pump coming in this week to beef up my closed loop some more so keep an eye out for the pics hopefully before the weekend. With that extra pump added, it should give me around 4,000 gph of flow (minus whatever headloss I will have) in about a 38 gal tank
