If you are going to have a block put in between the axle and the frame you may want to have a little longer block welded on to give you a little additional strength in the mounting area. Also, rubber torsion axles don't last forever. If you replace the axle, Flexiride axles have a torsion arms that are splined so that you can adjust the angle of the arm. The arms can work above level (no load), but 22 degrees down is a good starting angle but you can go as far as 45 degrees down.
Also, if the person doing the welding isn't familiar with building trailers, the rubber torsion axles are either bolted or welded, and if they are welded, you only weld around the part of the mount that is normally bolted and outward from there. You don't weld the mount near where the axle tube is welded to the mount. The axle tube needs to be able to flex.
