If you ever expect to tow the trailer again, you need to keep the proper air pressure in the tires or they will be damaged. What I would do is to place one of these under each corner of the RV. It would also help if we knew more about the RV. Noting is going to make it as stabil as a fixed house would be but there are some things that you can do.
If you don't ever plan to move the RV and if the park you are in doen't object, you could also lower the front down as far as possible and then put concrete blocks under the rear as near to the frame as possible. Then raise the front jack to push the fram down aginst the blocks, useing some wood shims as needed to keep it level side to side. Raise the front higher than needed and then place blocks under the frame there so that when you lower the front on to the blocks it will be level from front to back. That should support the RV as solidly as can be done.