As you know, water is weight.. But moving water in a 20 plus gallon tank can be a real problem.. I have and bolt a overland trailer.. Pulled by a 1998 Jeep Cherokee.. A single tank wasn't for me.. I have four 5 gallon containers that I can rotate as used or re filled that are in front of my trailer box and are on the tounge of the trailer.. I also have one 6 gallon container in the rear of trailer plus a 2 gallon Roto Pax that fills a space and two 1 gallons in my jeep..
Just for thought, I have four 2 gallon Roto PAX fuel containers on/in my roof rack.. Spare tire, Jack, shovels etc..
Obviously keeping water weight low in your truck would be best.. Slide out bed base? Take your time.. What works for me or others may not work for you.. Plan first.. Spend $ second..