Depends on the officer that stops you and how they interpret the law. If I recall correctly the book states under 10,000 lbs you can a single chain across the trailer in the front and a single in the back but there are some stipulations on the type of equipment that this can be done with. Your best bet is a chain and binder on each corner of the machine. Use G70 marked chains. Also don't forget the chain and binder on the bucket. Seems stupid on most applications like having to chain down a dozer blade. But, if you don't chain the bucket down you will get a fine for not having the implement secured.
I see a lot of guys using trailers that are to small and letting buckets and forks hang over the neck of the trailer. This is a very bad idea. You will also get a ticket for this. Not saying that is something you will do but I am just throwing it out there because it drives me crazy.