I know The Tribe 16 has made some custom belly skids for the Gladiator and JL Diesel. They also have a DEF tank and Exhaust skid (in stock). Call Lance Gilbert at (817) 945-2284, tell him Oliver sent you.
MetalCloak and RockHard both make diesel specific skid systems. Rock hard has an aluminum version. I believe Rusty’s and artec both have systems for the diesel in the works as well