Thanks Egon. Was thinking the same thing and will probably do it like yours.
Annealing relieves the internal stress of the material by heating it and allowing it to slowly cool, this is supposed to relieve stresses and pressures imposed during the machining process. Very similar to heat treatment used on steel or aluminum after machining. From what I understand if the material is under tension after bonding this stess has to go somewhere and will normally manifest as very small micro cracks otherwise known as crazing in acrylic. Annealing just allows the material to rebound to a normal state before it gets glued up. Have seen a lot of crazing in aircraft canopies and windscreens.
Here's the dilema.
I really like your idea of solvent cementing and then #42 along the edge. Maybe best of both here, it gets complicated though if using an outside beveled edge (which is what I was thinking if using 2 part) as there is not as much surface contact area for the solvent to work with just that little edge. Thats what Im concerned about if using both solvent and 2 part.
I like solvent because it welds the acrylic together, but with panels this thick and heavy preparing the edges perfectly smooth for solvent may be hard.
So was looking at the #40/42 option until I read that it had to be annealed. There is just no way for me to do this, so how safe would using #40/42 be without annealing since there is no molecular bond as in a weld? #40 also requires a vacuum chamber to suck out all of the bubbles in suspension after mixing. But I doubt if most do this, probably just mix and pour it. #42 is a good choice except it requires a really high dollar applicator gun to apply to ensure the correct mixture but still cheaper then the whole vacuum process. Was thinking of a slight outside edge bevel, building a dam around it with tape and pouring #40 or #42 in. See diagram.
#40/42 is attractive because it may be more forgiving of slight edge imperfections if the CNC dosent produce a perfect edge.
Have heard that CNCs are good at producing uniform sizes but not as good at edge prep. I suppose this would be entirely based on operator skill and knowledge.
The CNC prep work is getting done by a local shop. Hard to find anyone with a 10 ft table with suction hold down.
So I guess the real question is:
Should I use #40/42 without annealing using beveled edges and then route flush or... solvent cement only with flat edges using wire/pins method or... keep edges flat (no bevel), solvent cement and then use #40/42 along outside edge as fillet to prevent pushing out and then keep the bottom piece slightly wider to ensure the fillet has something to hold on to.
You guys are a big help and I hope this makes sense, thanks.
. Also even if u go with a solvent weld i would still tip the tank and glue each inside seam with 40. Really beefs up joint and looks pretty good. It should look like silicone but crystal clear. 
