Montana 3500/3400 ?

[Sam]

I have a 05 GMC 2500Dmax/Allison SRW purchased in May o5 to pull a 24ft. flatbed gooseneck and a fifth-wheel camper. I would like some ideas and thoughts about what I can pull and what I should buy from some of you experienced fifthwheelers. I already have my gooseneck on which I haul an antique tractor at a total trailer weight of 13,415 lbs.I do not know the pin weight, did not know it was a consern until now. I have had no problems with this load. I would like to buy a fifth wheel camper in the spring of 08 and be ready to camp in July 08 after retireing in June 08. Would be making short trips for the first year 300 miles max. My gooseneck hitch is a B&W and I would buy the Companion fifthwheel for the camper.
I have been to several RV shows and dealers, my first choice is a Montana 3500, second choice Montana 3400.
I have already upgraded my tires to 265/75/16 and installed a fifty gal. transfer fuel tank in the bed against the cab. Some time in the next 6 months I plan to install Firestone Air Bags on the rear axle. What ever I end up with I plan to order MOR/ryde suspension, MOR/ryde pin box and possibly disc brakes.
My truck weighs 4360 front axle and 3240 rear axle this includes the truck, myself,my wife and 30 gal of fuel.
Please share your thoughts and ideas and also if anybody knows the location of the fresh water tank on the 3500 and the 3400 hopefully I can adjust the pin weight.