Glad to know that isnt a Legends car, As a current INEX inspector I couldn't allow it to compete....too dangerous as well as illegal. Mounting the bottle in front of the seat would be ok, but I would prefer it to be mounted in the trunk area in case it should come loose....one less loose projectile in the cockpit during an accident. Smaller drivers whose seats lay back somewhat might have room behind the seat, but that makes servicing difficult at best. I strongly suggest the trunk area if possible. If it must be in the cockpit, use a solid, bolted mount versus a latch type that might come loose on impact.
When it comes to fire systems, if you think you cant afford one, compare the price to one day in a burn unit......its a no-brainer. I can provide a contact to a driver who wishes he had used one and can tell you the cost of an extended stay in the burn unit, he is still paying for his 10 years later and will be for the rest of his life.
Louie