Need help with selecting trailer length

I modified a firetruck and I'll be hauling small cargo trailers. My truck-tractor is 26' long (minus bumper). I have 7.5' of rear deck to mount my 26k 5th wheel hitch. I'm guessing at some point I'll be off the national network which I'm also guessing my max should be 65'? So 65-26=39. Add 4' or so for mounting/clearance for a total of 44'? Am I on the right track? Do I need to ask the company more questions about where they ship to? Thanks in advance.

 

Sorry, let me clarify. I'll be hauling small cargo trailers on a large trailer such as a wedge. I know on national networks I'll be fine, just off NN is my big concern.

 

Yes and no. Original gears were 4.11 on hard rubber mounts. I now have 3.55's on air with the possibility to go higher numerically. The trans isn't the best setup, but I only paid $10k for the whole thing with 18k miles. I'll have about $20k invested. Assuming I can scrap/ part out the rest, the truck itself will be almost free. And let's not forget the tires are like new, that's a chunk of change too. Ideally all of this will offset fuel costs at least in the short term. Original mpg was 5.5 @54k lbs. I've shed 36.5k, and will pick up 12-15k with my load. Also have switched to aluminum wheels, and the frontal area of this isn't much more than the hood/grill area of a regular semi. Probably the biggest change I hope to make are a different version of the same trans, and gears.

 

Ha! No I disabled it for my own best interest.