Prepare for ALOT of work. Measure three times to cut once. Patience is everything. Even with the best tools and facilities, it will take days to finish the body.
You will need plenty of material to fill in the bottom of the body. Since both of the guitars are "Strat" shaped, the bottom contours (where the
strap buttons are) won't line up flush. It will look like a rounded "W". You will need to fill this in with poly (or something similar), to make it flush. You will have to do ALOT of sanding to get everything smooth and even.
Not to mention, the wiring may be difficult, depending what you want.
I'd say look for a used Epiphone, Carlo Robelli, Rogue, Cort, Galveston, or something like that. It will satisfy your double neck craving and not kill your wallet (not to mention frazzle your nerves).
Cheers,
Butch