"2) The best steel to make a frame out of would have to be Chromoly IMHO, first of all its the strongest readily available steel tubing out there, and second for its corrosion resistant qualities compared to a regular mid to high carbon steel"
Anybody arguing the fact of chromo vs mild for corrosion resistance properties...turn and walk away. All forms of steel suck when it comes to corrision except for stainless.
I think it would be bad ass if you made the thing out of 4130, had it scoth brited down to remove all mill scale and then have it electorless nickel plated about .001" thick in a mid to hi phosphorus bath...you would be very impressed with the results....you would get corrosion resistance up to about 300 hours of salt spray which is about half of powder coat but powder coat isnt badass like nickel plating.