Not trying to hijack, but you gotta love the Sundown amps. Best amps I ever owned besides maybe the old Orion HCCA stuff.
As for the Alpine..I'd first try setting it up in the blazer as is (your going to wire it up anyway right?) And try positioning it in different locations. If you need help fine tuning your box for SQ, or starting over with some other design, those Thiel Small Parameters from Alpine regarding your specific sub would go a long way in helping you get the right internal volume and box type figured out. You could then modify Alton's design with your own internal bracing structure to make up any differences. I'd keep that Tarantula, not bad bang for the buck. You might need a new sub long before that Amp goes. I'm still using a cheap second hand Xstream 880.2 on an 18" eD woofer and it hits as good now as it did 5 years back.