New member first questions

Hi, new member here, I've done some lurking already, but now I have some questions of my own. I'm building a 6x12 single axle interstate roadrunner to to be a bit of a toy hauler and simple camper. I'll be towing it to Alaska, where I hope to build a small house, and live in this during construction. Kitchen up front, no bathroom, one half of bed folded up leaves a single bunk which can also be used for extra counter space, dining table, or workbench, everything in the rear hinged to fold against the wall to allow use as a cargo trailer for a motorcycle or just general stuff. I've been ordering parts and playing with some ideas on sketch up and have come to my first questions:
Weight distribution: I've laid things out the way I think they would fit best, but now I have to consider my tongue weight. Planning on a thirty gallon water tank -which I want inside for freeze proofness-, two gc2 batteries, and two 20lb propane tanks. With the idea of keeping the rear open, everything naturally fits forward or on the tongue. I have an F 350 to tow it, but I don't want to limit myself to a heavy duty truck just because of tongue weight.
Windows for thick walls: My current plan will end up with walls about 3.5" thick, and I can't find any RV windows for a wall this thick, any suggestions? I haven't looked at one in person, will using one for a thinner wall work and just leave a gap between the inside trim ring and the window? Or do the inside and outside bolt together to sandwich the wall?
https://vgy.me/GEaVHJ.jpg
https://vgy.me/fhefn0.jpg
https://vgy.me/6FP4T8.jpg
https://vgy.me/yIupMQ.jpg
Thanks -Aaron
Weight distribution: I've laid things out the way I think they would fit best, but now I have to consider my tongue weight. Planning on a thirty gallon water tank -which I want inside for freeze proofness-, two gc2 batteries, and two 20lb propane tanks. With the idea of keeping the rear open, everything naturally fits forward or on the tongue. I have an F 350 to tow it, but I don't want to limit myself to a heavy duty truck just because of tongue weight.
Windows for thick walls: My current plan will end up with walls about 3.5" thick, and I can't find any RV windows for a wall this thick, any suggestions? I haven't looked at one in person, will using one for a thinner wall work and just leave a gap between the inside trim ring and the window? Or do the inside and outside bolt together to sandwich the wall?
https://vgy.me/GEaVHJ.jpg
https://vgy.me/fhefn0.jpg
https://vgy.me/6FP4T8.jpg
https://vgy.me/yIupMQ.jpg
Thanks -Aaron