IamScout

Cut/dremel all of the internal supports for the stock internals until you are able to close the shell around the blastzooka tank. Ideally, have the stock blastzooka barrel match up with where the stock breech was.

Make room for the pump to come out the back

Figure out how to make the stock trigger hit the blast button on the blastzooka tank (you may need some sort of sheet plastic such as PVC or polycarbonate for this) or attach a separate blast button like what is described in this mod.
Glue the tank into the blaster (or figure out some non-permanent attachment system...polycarbonate brackets if you want to be really fancy, or maybe use epoxy putty to form a sort of cradle).

For some inspiration, check out:
http://nerfhaven.com...showtopic=22726
http://nerfhaven.com...showtopic=22767
http://nerfhaven.com...showtopic=19726

All of the aforementioned references are found in our Modification Directory, by the way...you may want to look there or search the rest of the forum for other "air tank in a new shell" modifications for even more ideas.

Thanks for the help!
And, yeah, probably could have just spent more time looking around, but I do appreciate that some people helped out.

Derek's Mod Center just did a video on this a couple days ago.

I, uh, kinda know that. Guess I forgot to mention that that was the video I was more like "I could do that" with. Unfortunately that video doesn't really talk on how he built the thing, or if it does, it does so very briefly.

I suppose I should add in my first two attempts here.
Modified Nerf Crossfire.

Modified Nerf Scout.
CrossFire Gets about 45 feet flat, while the Scout gets about 32 feet flat.