My suggestion would be to make a simple steel frame (proably 2" box or 2"x1" box section) same width as the floor pan and create it a little bit longer so you can make some brackets/arms going off to the (front subframe) lower fire wall mounts and the (rear subframe) front mounts. Use the same size steel for a leg in either corner with some corner bracing and maybe some large diamater (100mm+) castor wheels under each leg.
In this pic you can just see my stand under my van project. It's not designed to bolt to the vechile like you want but same idea. My legs are teliscopic so I can change the hight of the stand be about a foot. Also my castor wheels are a small size (50mm) bigger ones would be much eaiser to roll onto a trailer but the little ones are still useable.