there ARE some JUNK-As$ pre-fabs you can purchase. Also, you can buy the same type of enclosure a good builder can make. Looks like pro uses 3/4 mdf, classic is 5/8. Check for internal bracing, what ga wire is used, sealing, etc.
just listen to what you just said...i want a slot vented box and audo enhancers makes a custom one for the sub im getting