Contact Grippamax, they do a 400l based on their crashtested 650 and 1000l systems. Buy cheap buy twice, having seen the purefreedom crash test you can easily see that anything that isn't crash tested will not cut it. Your life, but cages are expensive to begin with, I think I paid over £400 when I had my old purefreedom 400l cage. Might as well pay more and do it once properly. I've got the Grippamax 650 now, just the tank and restraints and it's brilliant. I'm sure it will outlive me, it's bombproof.