On TTs in general, jacks are not used for leveling, especially on the lighter units. The frames are not capable of jack leveling, except fore and aft with the hitch jack. Lateral leveling is accomplished by careful siting of the trailer and using leveling blocks under the wheels. Jacks are used to stabilize the trailer lifting it a bit off its suspension to stop it from jiggling as people move around in it.
There are a number of schemes. The two best that I have seen are scissors jacks welded or bolted to the frame and 'stacker' jacks. I use both. On the front of my trailer I have a pair of scissors jacks welded to the frame. I can lower these without crawling under to set them. On the rear I use a pair of aluminum allow stacker jacks. I can easily place them under the frame and tighten them by hand as the frame comes back to meet the bumper at that point and is quite accessible.
I would not weld or fix any jack to the rear of most TTs. The rear ground clearance of your trailer is the clearence critical for surmounting driveway aprons and road traffic bumps. Both of my fixed rear jacks were trash within a few months of use and had to be removed. . If your axles have been flipped to provide more general clearance of the trailer frame, that might well be another matter, but with a stock set up, avoid fixed rear jacks. Stackers work just fine and are cheap and easy to store.