New step deck

I would have tucked it the 18". IMO you are not utilizing the 40,000 lb allowable on the trailer spread as much as you could be. You might find you are over axle on the drives and can't shift the load aft anymore. With the axles tucked, you can get 40,000 on the trailer and teeter-totter some weight off the drives to get legal.

I have a 3.5' tuck on the two 53's that I spec'd and nobody has laughed at me yet.

If I understand right, yours is 41' from KP to center of the 121 in "group". Same as mine.

 

I know a lot of guys that run 50 and 51's with 11ft spreads and 53ft with 12ft spreads set like yours. Know guys that got fined in fl, Ct and Tn for the 12's. The Ct fine was over a grand I think so he would only roll through at night after that. I know others that run their all the time and never hsd a issue with their 12ft spreads. I'd build a trailer just like you did, sounds like a very nice trailer. Good luck with it.

 

I keep a blanket permit for fl .dont go to cali.have not had a problem in tn running a 53