Or you could use two conventional oil seals and pack the area between them with grease. You would have the same overall concept, except in a two piece assembly.
I might put a conventional oil seal in deeper, maybe 1" past the Mad seal, and thereby have 3 outer seals. I think that should provide some good water/mud protection.
If your old axle shafts have normal rust or surface pitting, I think any of the above seals will get chewed up fast by surface irregularities, therefore it may be best do these seals with new axle shafts. Something I didn't give thought to until I pulled my axle apart and saw the shaft surfaces.