I seldom see snap binders on a lowboy and in my professional opinion that have no place on one. As far as tie downs go, what size chain are you using? Is it transport grade? As far as chain and binder count I always like to have half again as many binders as I do chains, mainly because they're most likely to break or malfunction plus you can use one long chain with two binders. Several short chains are handy in addition to your full 20 footers. On my big trailer I don't even carry a 20'. It will vary with your needs and uses. To me 5/16 has no place on a lowboy. Minimum 3/8 and I prefer 1/2. I was told a long time ago....chains in the headache rack don't hold a load on the trailer.
That being said, 20 chains on a load in the wrong spots don't do any good either. Biggest force you can apply to a load is a panic stop. Second, almost as important, is a side load like a curve too fast or an evasive maneuver. So think about those forces when you tie one down. Rubber tires loads I like to see more downward pull so as to compress the tires to mitigate some of the bounce. With a tracked machine you have to consider the coefficient of friction between tracks and trailer as well. May not roll but it sure could slide. Steel on steel, mud etc has an affect. I also always have a second set of chains that are purely a stop setup (as in panic). Always cross them if you can and at the same time pull forward and back at each end. Tires on a machine like you mentioned aren't too bad. Plus the weight end to end isn't bad. An RT crane, for example, is a little tougher to get down right because you have the cantilever affect of the boom as well as some big tires with lots of bounce. Sometimes the order you chain it down matters too. Also, depending on weight of load and deflection of trailer when loaded you may want to tie down after it's raised up, assuming an rgn.
So now that I've thrown a ton of info at you, I'd say minimum 5 on the tractor and 6 on the hoe. Each corner and through the middle on tractor, each corner and one on the boom of the hoe as well as on the front bucket. Overkill? Probably but I've hauled loads in excess of 200k payload all over the US and Canada for 15 years and have never lost one or even had a major shift after unforeseen circumstances. In my mind there's no "I'm just going around the corner". I'd be glad to help sort it out.