Kinda late to the party but I followed @ohanacreek on this one but added 2 subs and a Bluetooth marine amp to use mine & my wifes phone. I only have $156 in the amp and subs, $2 in fleece blanket , $28 resign, prob $20 in wood plus extra wood, screws and staples i had laying around.
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I didn't weigh it, wasn't to concerned about that. The 700's are top heavy as hell anyway. If your 6' or taller i wouldn't suggest building one with subs above your head. You will hit your head. I'm 5 10 and haven't hit yet. I almost coppied your T shape and extended the box into a rear section for the subs.
There is 3 different chambers sectioned off on mine and the corners were tough where the sub sections met the front 6.5" section. I stapled the fleece on the 1x2 slats and rolled them then screwed them to the backing. I'm very happy with it. I have to turn it off or tell the wife to turn it down quiet often.T shape was a pain to glass. The fleece just didn't want to stretch right