There are reasons axle makers and trailer mfg don't have or come OEM or have a option for leaf spring suspension blocks for heavy trailers. I've yet to find a professional big rig trailer shop that will add leaf spring suspension blocks without the owner signing a liability waver.
Trailer suspensions are subjected to much more side stress (twisting) issues than our tow vehicles......apples vs oranges.
I've had two of my rv trailers raised. One with longer adjustable 3/8" HRS side plate spring hangers. The shop charged my 230 bucks for material and labor.
I had a another shop fab and install a 3" sub frame for the 5er in sig. Total bill along with new suspension bushings and pins was 622 bucks.
