a "trunk" is a loose term... it all depends on the track.. and you are right.. what hondas have at a lot of tracks in my area is NOT considered a trunk... a trunk is a SEALED area seperated by a firewall or other rigid structure.. you can get the blowdown kit from NOS or whoever you want as long as it will hook to your bottles valve... on the bottle there is a valve and on the valve it has something that looks like a bolt with a hole in it.. under this bolt is somethign called a rupture disk.. its function is to rupture should pressure rise close the the maximum pressure of the bottle... in other words maybe the bottle can take 1800psi.. well that rupture disk is set at 1600 psi.. so it will rupture and release pressure BEFORE the bottle explodes...what a blowdown kit is.. is a plug that replaces that bolt and has a tube on the end and the tube is routed out of the car.. should the rupture disk pop the nitrous will be vented OUT of the vehicle... cars with rigid sealed trunks don't need this because the wall will prevent nitrous from seeping into the driver compartment.. our "trunks" are far from air tight.. so if you are planning on going to the track id get one.. if you plan on events id get one (sometimes the rules governing the event (tech inspection) is harder than normal track tech..

hope that helps..