93 4x4. Rot in frame cross member, does anyone make a kit for this. How would you address this?

 

IF....the frame is solid enough, I would cut it out and weld in a new piece of tube with fish plates on the ends.

 

I use a piece of tube , I think it was 2" .
cut out the old one as close to the plates as I could , and used a rasp on the hole threw the frame , slid the new tube in place and welded it in solid , then added the fuel mount and shock mounts