Well, my friend wanted to go from pneumatic tires to cushion tires and I told him that was a bad and costly choice.
I informed him today of the solid pneumatic option and he said he will look into that.

A solid Pneumatic tire would be the best bet in my opinion. are you talking about converting from pneumatic tires to cushion tires or just converting from air/tube tires,and going to a solid type tire,that is possible can use the Same rim and mounting hardware,solid pneumatics will last also

Thank you John.
I had already told him nearly the same about the cost of wheels and such to convert.
I will steer him toward contacting one of our local industrial tire dealers about the "solid tires on pneumatic wheels" option.

1. No approved option for such a conversion. Would be cost prohibitive it was - new wheels, tires, etc. Work with what you have.
2. The buyer could buy solid pneuamtic style tires - best long term choice.
3. Yes, air type pneuamtic tires can be foam filled - but you need to find out what the total cost will be, plus the truck will be down for some time as the foam filling must requires a curing time & usually this cannot be done on site. A limit to foam filling is if there is a cut in the tire (liek a side wall cut teh foam will escape).

Contact a local industrial tire company to help you with this project.