Hate to go against everyone, but rachet straps can and will get cut on sharp metal edges and the movement of tied down load on the road. They are not the best tool for this kind of job and the weight of the item being tied down. Trust me, YOU DO NOT WANT A LOAD GETTING LOOSE IN TRANSIT. This is not hay you are moving.
We haul machinery and you want to use chains with hook ends, with chain binders to secure your spreader in or on the trailer. Chains won’t cut thru if rubbing on metal edges during hauling. If there is a rental store nearby you could rent the chains, needed chain binders, and probably get a free lesson on how to tie down the spreader to be in compliance with laws regarding hauling equipment. These folks move large equipment all the time, should know the laws regarding safe movement on the roads. For our big backhoe, each of the corners must be chained securely. Recommended to also secure the bucket and hoe with their own chains and binders in case of rough roads.
I would get some 4x4 or 4x6 wood pieces that are the width of trailer. I would SPIKE THEM to the trailer floor in front and behind the wheels, to aid in keeping the spreader in place on the trailer. You will need large spikes to go thru that thick wood and go deep into the floorboards of trailer. Take a larger hammer, 4# or larger size to drive the spikes, your carpenter hammer won’t do it. You will need a pry bar to remove the 4x wood after getting home. But better to keep things where they belong, than be sorry about it later. This applies to the chains over rachet straps as well.
The driver is ALWAYS responsible for their load. Making sure it is firmly secured, can’t turn into problem while enroute to the final destination IS YOUR RESPONSIBILITY. You do not want it to be your fault the ill-secured load gets loose on you or hurts someone else.