On our previous 5th wheel I had one of the big bubble levels on the fifth wheel mounted so I could see it from the driver's seat, for
side-to-side level, and a smaller bubble level mounted on the side near the stabilizer switches for front-to-back level. Used a 3 foot
bubble level to get those calibrated initially and never messed with anything after that.
Apps are kind of a cool thing, but you would have to go inside, see how level it is, go outside, make adjustments, go inside, see how
level it is, etc. Easier to go old school with this particular chore. JMO of course.