Re: Replacing Axle. Lifting Boat/Trailer up to work on it Safely....
Use jack stands (aka: axle stands) under the frame rails. Use 1 near front of leaf spring bracket. Use 1 near the rear of leaf spring bracket. And, use tongue jack to steady the tongue area as well. If doing this outside, ensure lifting on level ground, its firm ground (not on soft dirt) and no wind. Windy day on jack stands adds extra danger risk. As others stated, lossen all wheel nuts, leaf spring eye bolts, U-bolts before lifting onto jack stands. If U-bolts and/or leaf spring eye bolts are too rusty, simply electric grinder them off - instead of using force while on jack stands. Too much force while on jacks is like a windy risk thing. After new items are installed, firmly tighten, let down (off jack stands), tow loaded trailer around the city block a few times (to allow things to "settle in"), then torque down all bolts / nuts.
Hope this helps..