towing 9,000 lb camper 13 hours

Hello, there. I'm new to this site. just found it. I have a 2 door 3 seater f250. I tow my palomino puma with that truck. I am looking to upgrade the truck to 4 door just so I can carry the family camping and not drive 2 vehicles. Im deciding on gas or diesel. for short trips its no big deal driving 2 cars. but I want to go to key west which is 13 hours from me. id like to stay with a gas just because I'm used to it and its cheaper. This truck will be used for my every day business as well. i turn off and on the truck 25-30 times a day. My question is does this weight for a bumper pull put too much strain on the gas engine with 6 people in the truck? would you stick with gas or swap to diesel? will starting and stopping a diesel motor 30 times a day 5 days a week hurt it? I appreciate all info. I need all the answers I can get as this is going to be a big decision for me. thanks y'all!!! happy camping