Is it ok to just let it sit on the tires or should I put it on a stand? I remember reading somewhere that you will get more life out of your shocks if you put it on a stand. Is this true?

I just throw mine on the floor and let it sit it shouldn't hurt it one bit just make sure you have drained any excess fuel out of the tank and put in some after run oil I use marvel mystery oil way cheaper and does the same job. Of course if your shocks are leaking oil then I'd put it on a stand so you don't have to add oil every time you go to use it

IF it were an onroad car, I think it will matter more.

But still, what you say is correct. To avoid deforming the wheels, leave it up such that the weight is supported by the chassis and not the wheels alone!

-ram