I carry a few 2x10 short pieces with a bevelled end. They are just long enough to stack 2 up to make a ramp. I back or pull onto the stack with the good tire which raises it about 3-4 inches. I use the bottle jack from my Dodge and have other small stackers for the jack. I have an overslung suspension on my trailer so there is no flat plate just the axle and U bolts. I keep a slotted piece of 2x4x4" for the axle to jack. Had to use it this spring by the side of the I75 outside of Atlanta.
Do your self a favor and check your entire system, spare wise ie test run dropping the tire and removing it from the rack holder. I had a few issues with rusted parts..not something you want beside a busy Interstate...