Our trailer is on a seasonal site for the last two years. I have 8' lengths of 2" x 10" under the tires, patio stones under the stabilizers and a concrete block under the tongue jack. Our site is quite level so that does it for us. I didn't see the need to block up under the chassis due to the length of our trailer but our friends who own a 40' park model did and I would recommend the same. Just remember that if your trailer has stabilizers they are just that - do not use them to jack up your trailer to level it as you may/will twist the frame
. What trailer do you have and how is your site for level?