No matter whether you use uHaul padding or batting as the middle layer, they both need to be encased in fleece. I have some pads and liners that are seven years old, but I can tell that the uHaul pad is worn out in the liners because it has ceased absorbing the urine. How long they will last depends on the frequency of use, and whether or not you use bleach in the wash.
Like @bpatters, I used to think that fleece is indestructible until I began using bleach every wash. It has managed to reduce my liners to tatters! I don't recommend using bleach except every 3-4 washings. The rest of the time I add either Borax or OxyClean to the wash. I have a rinse-and-spin cycle on my washer, so after the regular wash is finished, I pour copious amounts of white vinegar on the items and run it through another short rinse-and-spin. Works wonders for residual odors. lol