I could use a little advise, Last year I bought a Windmill palm and built a box like the one that Antitropical uses, it worked great a little brown of the ends of some of the Fronds but in good condition. This year I bought two Sabal Birminghams and a Sabal minor. I am limited on space so I was wondering if anyone could tell me if a portable greenhouse with heater would work? I am looking at one that is 12x7x7. This would cover all three trees. Also how often does everyone fertilize? I live in zone 6 and it gets down to zero dergrees here somtimes once or twice a year.