Around here we drive the beach a lot. for years people use old drain oil and spray the undercarriage completely, drive a dusty road and repeat occasionally. Seems to work well. you get a bit of a build up after a while. If you ever want to, you can powerwash it all off.. just a thought

 

I have used that too its hard as nails! But on an offroad vehicle it's too expensive to get scraped off llmao! But be sure to st a spray gun and borrow a shop with a lift makes life so much easier!!!! And don't let it on your skin! Stays forever!

 

Around here (WNY) since we live in the rust belt, Schmidt's Auto Body does a Heavy Grease/Oil coating on the undercoating & in doors and such. Works wonders, paint just cracks and chips then rusts.
This stuff costs about $100.00/year. Pretty cheap insurance. My XJ is from PA (less salt used) this fall I'll start my $100.00/year undercoating...... See if there are any collision shops that have this undercoatings. Here is the link, give them a call, then you could call around....

Good luck, keep your XJ cancer free...
http://www.schmidtsautobody.com/

 

Seems like a good idea and can be pretty cheap if you use used oil.