I'm pretty sure everyone uses TP for one reason or the other. I don't know if it's normal across all manufacturers and all models, or if it's due to the fact the Oasis is a low end model, but ours didn't come with at TP holder. I was struggling to find a suitable support for one in the bathroom, I was hoping to not have to mount a holder behind me whilst seated, nor did I want it on the "shower" side of the bathroom; a soaked TP roll isn't my idea of a good time. Wall opposite the shower is SUPER flimsy - it doesn't appear to be attached anywhere in the plane of the wallboard, only on the edges. I decided to do a little investigation by taking off the light switch and was delighted to find a piece of wood back there - I think it's a 1 x 2.
Using this new-found knowledge, I decided that would be an acceptable location. Having read elsewhere on the forum that mounting the TP vertically helps prevent unraveling, I went ahead and placed the template vertically, drilled my pilot holes. one pilot hole for each leg of the holder went into the lumber, and one just into the wallboard. Four screws later I ended up with this. (Again the product is from Wally World)