I just took the body off a 1972 Compact Jr, so it's not the same trailer as yours, but it should be the same general process to get your body off the frame as mine was.
Very important: BLOCK YOUR WHEELS front and back on both sides while you're doing this, so they cannot roll either way! Be sure you're in the spot where you want the body to sit while the frame is gone.
Working with the trailer parked on a level surface, I located and removed all the bolts holding the body to the frame. Then I placed jackstands under the rear two corners of the body, using small scraps of plywood to protect the fiberglass. Then I slowly cranked the tongue jack to raise the hitch of the trailer.
As I did this, the back end of the frame dropped away from the fiberglass body, which was temporarily supported on the jackstands. When I had a sufficient gap between the body and the frame, I slid a 2x4 into the gap. Then I cranked the tongue jack to drop the hitch back to a level position, which raised the back end of the trailer off the temporary jacks. This left me with the rear of the body resting on the 2x4, which was sitting across the frame. I removed the temporary jacks, and did the same for the front of the body, placing the jacks under the corners, dropping the hitch (instead of raising it), sliding in the 2x4, then raising the hitch to level and remove the temporary jackstands. This left me with the body of the trailer sitting on two 2x4s, which in turn were sitting on the frame of the trailer.
Now comes the fun part. I rounded up some cinder blocks I had, but you can use whatever sturdy objects you want to support the body of your trailer. First drop the front of the trailer by several inches (which raises the back of the trailer) and place the cinder blocks underneath the protruding ends of the rear 2x4. You need to place them wide enough to make sure that the frame will clear the blocks when you pull it out from under the body. Then raise the front end of the trailer until you can place the cinder blocks under the front 2x4 as well. Watch the rear of the body while you do raise the front, and make sure its 2x4 settles solidy onto the cinder blocks back there. Now lower the front of the trailer so its 2x4 settles onto the blocks.
What you should end up with at this point is the body of the trailer supported on 2x4 cross-members which are resting on cinder blocks. The body should be sitting a couple inches or more above the top of the frame when the frame is level. Give the whole thing a good walk-around and make sure it's firmly seated on whatever type of blocking you put under it. You will put more support under it after you've removed the frame.
Next, loosen the lug nuts on your wheels, and jack one side of the axle
up just enough to remove the wheel. Be careful not to jack it up so far that you hit the body and move it. You only want to lift the frame a small bit to clear the wheel off the lug bolts. Now you want to cut two circles of 3/4" plywood to serve as temporary wheels. You will need to measure to see what the smallest circle you can use that will prevent your axle
from dragging on the ground. Drill holes in the appropriate spots for the lug bolts to pass through, and bolt the plywood 'wheel' to your hub. Do the same for the other side.
This should leave you with the frame sitting low enough under the fiberglass body that you can carefully pull it out, rolling on its tiny, temporary plywood wheels. Once you have the frame out from under the body, place more support under it using wood blocking and cinder blocks, or whatever you have that will help support the body. What I did is put a 2x4 along the length of the body on both sides, and put jacks under each end of it to support the long sides.
Replace the tires/wheels on your trailer frame, and voila...you're done. I'm a small person, only about 125# and I managed this job on my own, so it's something I think most people can do by themselves if they need to. It would have been nice to have a spotter at times, so I didn't have to walk back and forth around the trailer checking things all the time, but it wasn't necessary by any means. It took me about 2 hrs to go from removing the bolts, to pulling out of my driveway with the frame to take it to the welder.
Good luck, you can do it.