Hi, i am robobd, and i just replaced my floor on my 88 22L to see where your floor joists are, crawl under the trailer from the back or side. let me start over, first determine what parts of your floor is bad. I used a larger flat end punch, and used my hand to push down on the whole floor to determine all the soft spots, then I used a magic marker to out line the soft areas. I then measured from the back wall to the edge of the soft spots I marked, then I added two more inches to it. I then measured from my street side wall (which was bad on my hi-lo) to the edge of the soft line , then I crawled under and measured under the trailer to see how far over was the floor joists, went back inside and transfered over the lines where the joists were. remember there is an inch difference (wider) from your inside measurement. to make sure, measure 3 times, and cut one time. I also went under and drilled up right next to the joist on my short side to determine how far over to cut, then measured from the inside, added a 1/2" to determine where the center of the stud is. marked where the cut needed to be , I used an osolating cutting tool from harbor freight (39.00) and cut a 1/4" depth at a time so I would not cut my black water tank. please read my other post on soft floor.
If you have any questions, pleas ask no matter how small it may seem, an unkown answer could be the difference between $!.00 or a $1000.00 if not knowing how to do it!
1999 ford f250 7.3 diesel