Going Flatbed and Need Some Setup Advise

For flatbed work its like a woman wishing for her dream kitchen, you can never have enough cabinets. But for your answer, yes a single side box and a rack is a good start.

With a rack holding chains/binders, tarps in the box, bungees hung from cross members, dunnage stowed in dolly bracing, 4" straps wound on ratchets, 2" ratchet straps under sleeper, edge/corner protectors under other sleeper side, coil racks sitting on dash, magnetic oversize lighting, flags, and sign-age inside the sleeper, wife, trainer, or pets strapped firmly to bed, and a full case of 5hr energy drinks buckled into passenger seat... you are now ready! J/K

Another storage location I rarely see used is a drop in box between the frame rails of the tractor (headache rack sits on top of its flanges) perfect for ratchet straps and corner/edge protectors.
24"L x 22"H x 8"D Aluminum In-Frame Tool Box

 

I have an open rack with chain hangers and trays, along with the in frame box. I have never had an issue with my stuff growing legs in the dark of night.

And what @TheDude1969 says about never having enough storage is spot on...I have 5 boxes on the trailer, the headache rack, in frame box, and two saddle boxes. And I can still think of things I wish I had room to carry.

 

You might check a place called Chuck Henry in KS on I-70 between Salina and Abilene. When I was looking last year they had pretty good prices. But you may be better off looking on Craigslist for someone cashing in their chips.

 

I preferred the open rack for the obvious price diff, and the chain racks do have lids you can padlock.

 

Something else to consider that may give you issues on your choice(s) for your head ache rack... (forgive me if the mental image I'm trying to word is confusing) Is the distance between rack installed, and the front of the trailer..

This is important because, you need to know the forward most position of the fifth-wheel, with a full load that keeps your steers legal. This becomes a problem on many trucks that were designed for the tightest air gap (truck to trailer) for economical reasons, and even shortens the distance more so if you have conventional exhaust stacks.

You can imagine that a cabinet, or bottom tray will lessen that distance even more. The only remedy is a shorter pin length. <--- I found out the hard way, ouch$$$

 

I know on mine I keep the fifth wheel slid all the way back, not so much for the front of the trailer to clear the headache rack, but for the trailer frame drop and landing gear to clear the mudflap hangers on turns. Before I had all these boxes on here one time I tied the tarps down to the catwalk. Worked fine until I cornered real tight and ripped a hole through about 6 layers of the folded tarp.