The screw-type leveling jacks used with a travel trailer make it pretty simple to set up a frame level, or at whatever rake angle you want. Installing some large anchor bolts in a concrete floor allows a chassis builder to anchor the frame down with ratcheting chain binders for a really solid base to work from. We used 1" diameter female thread sockets installed into a level floor when building or repairing race car frames. When the surface plate was not in use, just unbolting the chain anchor points made that bay useful for general maintenance work.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!