I have an assortment of PVC pipes cardboard rolls and specially formed sanding blocks. No store bought 'contoured' blocks.
They make a contour or radius finder that comes in handy. (google it) It allows you to copy any curve profile and transfer it to, in my case a 2" thick piece of that pink or blue styrofoam insulation board. Then I use adhesive spray and stick my sand paper to it.
I made some from Ipe wood scraps first but that was a LOT of work.
The convex curves of the fenders changes from front to back so I picked a middle of the fender point to get my 'copy' and find that by simply using the top, bottom or reversing the block gets me real close on the Outer curves.
The concave inner curves worked best with the 12" long variety of PVC or cardboard tubes. Whatever fits best.
For cutting the filler and primer I used 80 up to 220 grit on the sanding blocks. Once I get it straight I switch to simple 'soft pads' and work up through the grits with them.
