off grid grow box

i was planing on running my grow off osme small boat motors. I am planing on building a small box for 4 autoflowering plants. i was going to run a 150 mh for veging and 200w hps. i got 2 small computer fans for a in and out for ventalation. i will insulate my box it will only be 6 feet tall and 3 feet wide and 6feet long. I was wondering if i could use a mr heater on low to heat my box outdoor during winter. i was going to charge battery at home and get 2 batterys so i never run out of power. i got a 500w regulator so i dont have to geato rig and wires. im sorry if my spelling is bad i am dislaxic and only good at physical labor and sports. this will be my 2 grow but grew outdoors befor so first attempt indoors.

You may need more than a couple PC fans for ventilation, and a 4x4 area might make more sense as far as light distribution is concerned. As far as the heater goes, there's only one way to find out... try it.

i think i wont insulate it so the heater wont get it to hot i will go with 4 cfls over a small corner of the box other side is for battery and inverter. it should be a fun stealth auto flowering box just for personal. far from my house no one will find in woods. just don't want box to get 100 degrees from heater haha. i will need a bigger fan but want to keep sound down. what is a good fan? but it has to use little electricity. i want to get solar panels and go full grow with little Honda generator for dark. but got to start out small and get use to growing. i got wood for box going to build soon might put up pics of my grow so you can help. im going to go with nirvana's auto flowering northern lights.