My question is, are there any diy kits out there that will allow me to get a
nozzle into the cavity and fill with foam? Doing this much space won't be
cheap, so I would need a bulk kit of some sort.

I've googled a bit and only come up with companies that do the job for you.
I'm more than capable of doing the job myself.


Yep, try Tiger Foam:

http://www.tigerfoam.com/

--
Dennis