Tires: 2003 Dodge Ram 3500 quad cab single wheels, dodge ram 3500, stock tires

Question
I use this truck almost exclusively to fish on the beach and  I carry a Lance slide-in Camper on the pick-up bed that weighs about 3600 lbs.  In order drive on the beach I have had to lower my tire pressure to 20lbs psi.  I have done this for 7 years and have put 30,000 miles on the truck.  The stock tires on this truck are 265 70R-17 E load Range. Needless to say the sidewalls are cracked and ready to fail and I need to buy new tires.  I wanted to go up a size perhaps to 285 70R-17 but tire dealers say the only size for my vehichle is the 265.  I spoke to my mechanic and to someone at tirerack.com and they assured me most likely I could get a 285 on my truck no problem.  My questions to you are:
1. Do you think my truck could accomodate a bigger tire?
2.  Will a 285 give me a sufficient increase in my floatation on the sand and will it allow me to lower my tire pressure to a more reasonable PSI?
3.  What is the biggest tire that I could put on my truck without more sigificant modifications?
4. Are there modifications I can make to accomplish my goals short of making my truck a "Monster truck"?

Answer
John,

First, Tire Rack is probably in the best position to recommend what will fit - that's their job and they do it well.  They actually measure vehicles - something I just can not do.

I am of the opinion that increases in tire size have to be large to be effective for sand flotation - and the change you've proposed is kind of minimal in that respect.  But I also think you don't have much in the way of options - unless you want to seriously alter the truck.