Support, support, support. Think leverage. You need the bearings as far outboard (as close to the wheels) as you can possibly manage. Then, if it's a fairly wide axle or subjected to off-road-esque forces, extra inboard support may be in order.
there butted up to the hubs not even an 1/8 of an inch using a azusa 44inch flexpruff axle but have one pillow block in the middle thinking about putting one on each side of the middle has about 18 inch gap