Jump on the Zv4's while you have the chance. You have obviously already heard them at the competition and I assume that you liked the way they sounded in their vehicle. This also saves you time and effort building an enclosure (assuming it fits in whatever vehicle you have). You do have a Sundown 1500.1 so its not like they aren't going to move. you will save money buying the subs and box alone because roughly $600 a piece/ Zv4 + time, planning, materials, craftsmanship that goes into making a box... I feel like get the subs, run it off of temporary power that already works with the electrical you have and, as time progresses, build on electrical and buy another/ new amp.