Transfer flow is a well known company that mfgs aftermarket tanks. Either as replacement tanks or additional tanks that fit in the bed of your truck. I chose the 45 gal. replacement tank. Have a friend who is good with cars. We popped out the old and put in the new. The new tank is steel and weighs in at 150 lbs. You can't do it by yourself. Even if 150 lbs isn't heavy for you, it's hard to get leverage on it laying on your back. Just go to
www.transferflow.com. They also advertise in Trailer Life Magazine and most all other RVing publications.
I'm very surprised you are in Gulf Shores. The state park there is one of our very favorite places to stay and it was ruined by Hurricane Ivan. You must be at Gulf Breeze RV Resort just across from the Woodlands Golf Course.
Hope this will point you in the right direction. By the way...I was most pleased at how well my Duramax pulled the 3255RL. It is some 2000 lbs. heavier than what we traded and I can't tell the difference. The Montana actually tows better than the Gulfstream product we traded. Never another Gulfstream.