I just made the switch almost a month ago after 4 and a half years of dry van only...all I can say is I can't believe I haven't done this sooner! For me, this is way more fulfilling.
Got tired of the sag in my 60" box and all my spare straps rolling all over the place, so I took care of both at the same time. The wood is all 2x6 pine that I made fit snug with a pruning saw and die grinder, and it's all held together with 4" screws I had to trim where needed, and a few strong ties. Once it was in (it was a tight fit) I went underneath with a bottle jack and some 12" plates, and used 4-8 screws a board to suck the bottom of the box back up where it needed to be. Note that it's square I'll have the corners welded back up, and get some new T-handles and weatherstripping so I can actually have another water tight box on the truck.
My best tip is don't unless it pays a lot more then don't. I'm making more now just sitting in docks all day then I ever made running cranes on flatbed trailers. Easier work. More money. Less bad weather. What's not to like?
I'm making 2-3x more than I used to, and have a good laugh watching door swingers running around fighting over $1.20/mi loads.
Great detention agreements, I'd imagine. Last week I ran a 15 mile load paying $500 linehaul, and ended up with $500 in detention by the end of the day. But that was at a windfarm, and they'd have trouble crane loading a van like that.
Got started on my smaller box with the scraps left over from my big box last week. This box actually has a steel frame, so it wasn't sagging, but it was super cluttered. I had enough wood to make this rack for my binders (well, 9 of them, at least) up, and when I can grab a bit more wood later I'll box out the channel the handles move through so I can fit all my short chains and loose hooks in the hanger without getting in the way of the binders. I'll box out the rest of the box into squares so I can throw all my chains in and keep all my other equipment on top. I should have gone through my boxes and done this years ago.